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In this Letter, the p-GaN high electron mobility transistor (HEMT) with hybrid drain of recessed Schottky (RS) and p-GaN isolation blocks' drain (HSP drain) is proposed and fabricated for good reverse blocking capability. The related operation mechanism has been investigated and revealed. The proposed device features a drain terminal consisting of the array-distributed recessed Schottky and p-GaN isolation blocks. Based on the features, the reverse leakage current (5 × 10−9 A/mm at VDS = −100 V) is obviously reduced by two orders of magnitude compared with that (5 × 10−7 A/mm) of p-GaN HEMTs only with recessed Schottky (RS) drain, which is the lowest leakage current among the reported GaN-on-Si reverse blocking transistors. The introduction of these p-GaN isolation blocks has a negligible impact on Von (Von = 0.63 V). Therefore, a good improvement in the trade-off between the reverse leakage current and Von could be achieved because of the significant reduction in the reverse leakage current without sacrificing Von. In addition, the reverse breakdown voltage of −800 V at 1 μA/mm with a substrate grounded in the proposed device is evidently improved compared with the counterpart (−680 V), which is attributed to effective alleviation of the high electric field near the HSP drain. These results demonstrate the significance and potential of p-GaN HEMTs with HSP drain in reverse blocking applications.

The construction of Ga2O3-based p-n heterojunction offers an alternative strategy to realize bipolar power devices; however, lattice mismatch usually leads to undesirable device performance and makes interface engineering more challenging. In this work, we demonstrated the construction of lattice-matched p-n heterojunctions by the in situ hetero-epitaxy of p-type α-Ir2O3 on n-type Si-doped α-Ga2O3 using the mist-chemical vapor deposition technique. The α-Ga2O3/α-Ir2O3 p-n heterojunction shows single-crystalline corundum structures and well-defined rectifying characteristics. The transport mechanism has been identified to be space-charge-limited current conduction, which is induced by interfacial traps in an ultrathin disordered layer at the α-Ga2O3/α-Ir2O3 interface. Through thermal treatment in oxygen ambient, interfacial trapping states are suppressed, and more shallow acceptors of Ir vacancies are activated, both of which lead to the profound reduction of reverse leakage current, thus the improved current rectification ratio. The p-type α-Ir2O3 with advantages of lattice matching to α-Ga2O3 provides a promising strategy to realize high-performance bipolar power devices.

Reliability tests involving the application of high electrical stresses were employed to assess GaN-based vertical p-n junctions fabricated on freestanding GaN substrates with threading dislocation densities less than 104 cm−2. Electric field crowding at the device edges was eliminated by employing a shallow bevel mesa structure, thus allowing an evaluation of the reliability of the internal p-n junctions. The p-n diodes exhibited reproducible avalanche breakdown characteristics over the temperature range of 25–175 °C. No degradation was observed even during tests in which the devices were held under a reverse bias near the breakdown voltage. Despite this high degree of reliability in response to reverse bias stress, a small number of diodes were degraded during continuous forward current tests, although the majority of diodes remained unchanged. The reverse leakage current exhibited by degraded diodes was increased with an increase in the forward current density within the range of 50–500 A/cm2, while the breakdown voltages were unchanged in response to current stress. The leakage level increased exponentially with an increase in the total amount of injected carriers but eventually plateaued. In the degraded p-n diode, a luminous point in an emission microscope corresponded to one of the threading dislocations observed in the synchrotron x-ray topography, indicating that a specific dislocation played as a leakage path after injecting carriers.

The development of gallium nitride (GaN) power devices requires a reliable selective-area doping process, which is difficult to achieve because of ongoing challenges associated with the required etch-then-regrow process. The presence of silicon (Si) impurities of unclear physical origin at the GaN regrowth interface has proven to be a major bottleneck. This paper investigates the origin of Si contamination at the epitaxial GaN-on-GaN interface and demonstrates an approach that markedly reduces its impact on device performance. An optimized dry-etching approach combined with UV-ozone and chemical etching is shown to greatly reduce the Si concentration levels at the regrowth interface, and a significant improvement in a reverse leakage current in vertical GaN-based p–n diodes is achieved.

In this paper, high performance lateral Al0.85Ga0.15N Schottky barrier diodes (SBDs) with a field-plate structure and a heavily doped GaN cap layer in the Ohmic region are demonstrated. Employing Al0.85Ga0.15N rather than AlN for the channel layer effectively reconciles the tension between electron mobility and dopant activation caused by AlN material dilemma. The lateral Al0.85Ga0.15N SBD with an anode-cathode spacing (LAC) of 20 μm achieves a specific on-resistance (Ron,sp) of 0.19 Ω·cm2 and a breakdown voltage exceeding 3 kV, rendering Baliga's power figure of merit of more than 47 MW/cm2, which is the highest value among all AlN- or Al-rich-AlGaN (Al ratio > 70%)-based diodes. Reverse leakage current mechanisms of Al0.85Ga0.15N SBDs are dominated by a variable range of hopping and trap-assisted space charge-limited conduction before destructive breakdown occurs in the field-plate oxide, which are verified by analyzing the reverse leakage characteristics. Combined with the stable performance with temperature up to 275 °C, the Al0.85Ga0.15N SBD shows great promise for next--generation high power electronics applications after further resolving the Ohmic and electron mobility issues.

In this paper, we show that high-performance β-Ga2O3 hetero-junction barrier Schottky (HJBS) diodes with various β-Ga2O3 periodic fin widths of 1.5/3/5 μm are demonstrated with the incorporation of p-type NiOx. The β-Ga2O3 HJBS diode achieves a low specific on-resistance (Ron,sp) of 1.94 mΩ cm2 with a breakdown voltage of 1.34 kV at a β-Ga2O3 periodic fin width of 3 μm, translating to a direct-current Baliga's power figure of merit (PFOM) of 0.93 GW/cm2. In addition, we find that by shrinking the β-Ga2O3 width, the reverse leakage current is minimized due to the enhanced sidewall depletion effect from p-type NiOx. β-Ga2O3 HJBS diodes with p-type NiOx turn out to be an effective route for Ga2O3 power device technology by considering the high PFOM while maintaining a suppressed reverse leakage current.

We report on the growth of n-GaN/p-Si heterojunction solar cells via thermal chemical vapor deposition on Si (100) substrates at different growth temperatures (900, 950, and 1000 °C). The influence of growth temperature on the morphological, structural, optical, and electrical properties of GaN films has been elucidated. Increasing the growth temperature was found to reduce the internal stress and improve the material's crystallinity as confirmed via x-ray diffraction and Raman spectroscopy analyses. The photoluminescence spectra exhibit strong near band edge peaks in the range between 375 and 366 nm, with the peak intensity increasing with increasing the growth temperature. The current–voltage (J–V) characteristics of the assembled heterojunction solar cells showed the reverse leakage current to decrease with increasing the growth temperature. Consequently, the solar cell fabricated using the films grown at 1000 °C exhibits higher conversion efficiency (8.17%) than those grown at 950 °C (5.15%) and 900 °C (2.48%), respectively. This work shows that the structural, optical, and photovoltaic properties of the grown n-GaN/p-Si heterojunction solar cell structures are strongly influenced by the growth temperature.

Very high temperature operation β-Ga2O3 Schottky contacts were fabricated on moderately doped 2 ¯ 01 β-Ga2O3 single crystal substrates using four different types of intentionally oxidized platinum group metal (PGM) Schottky contacts (SCs), i.e., PtOx, IrOx, PdOx, and RuOx (x ∼ 2.0, 2.2, 1.1, and 2.4, respectively) formed by reactive rf sputtering of plain-metal targets in an oxidizing plasma. All four types of oxidized PGM SCs showed rectification ratios (at ± 3 V) of more than 10 orders of magnitude up to 300 °C, with almost no measurable increase in reverse leakage current density (Jrev) from that at room temperature. From 350 to 500 °C, a measurable increase in Jrev was observed, which was consistent with the thermionic emission of charge carriers over the respective image force (IF) lowered Schottky barriers. Despite this increase, PtOx(IrOx)[PdOx]{RuOx} SCs showed large rectification ratios (at ± 3 V) of 6 × 106(8 × 106)[5 × 105]{2 × 104} and IF-corrected barrier heights of 2.10(2.10)[1.90]{1.60} ± 0.05 eV, respectively, while operating at 500 °C. The significantly lower 500 °C barrier height of the RuOx SCs was due to the thermal reduction of RuOx to Ru that occurred above 400 °C. In contrast, the Schottky barriers of IrOx, PtOx, and PdOx SCs were thermally stable while operating at 500 °C, indicating significant potential for their use in very high temperature rectifying devices.

We utilized ultra-high sensitive emission microscopy to investigate the origin of reverse leakage current of edge-defined film-fed grown (001) β-Ga2O3 Schottky barrier diodes. In the emission patterns, we observed a partially appearing void, having a typical width and depth of 300 and 83 nm, respectively, with a base angle of 75°, below the Schottky barrier contact on the β-Ga2O3 surface. Simulations show that the electric field at the bottom of the void reached 9 × 106 V/cm at a reverse bias of −60 V and in the case of an ideally flat surface 3.1 × 106 V/cm. This indicates that the reverse leakage current originates from an electric field concentration in the partially appearing voids on the surface. On the other hand, we have confirmed that there is no clear relationship between the leakage current path and the dislocations observed by synchrotron x-ray topography.

The early stage degradation of electrical properties in AlGaN/GaN high electron mobility transistors (HEMTs) under fast neutron irradiation is studied. After the 1 MeV neutron irradiation at a low fluence of 1 × 1014 neutrons/cm2, the reverse leakage current decreases while the output and transfer characteristics remain unchanged, which cannot be explained by the previously reported high-fluence degradation model. By employing temperature-dependent gate leakage current measurements, we show that the dislocation related Poole–Frenkel (PF) emission dominates the gate leakage mechanism before and after irradiation whereas the barrier height for electron emission to conductive dislocation increases after the neutron irradiation. A model with the evolution of dislocation from the VGa-decorated configuration to the pure configuration is proposed to describe the degradation of AlGaN/GaN HEMTs at the low-fluence early stage neutron irradiation. This model enriches the understanding of the degradation mechanism of neutron irradiated AlGaN/GaN HEMTs.

We investigate the intrinsic reverse leakage mechanisms in Ni-based Schottky barrier diodes (SBDs) fabricated on a ( 2 ¯01) single crystal β-Ga2O3 substrate, where a uniform bulk reverse leakage current has been designed and confirmed. The temperature-dependent reverse leakage characteristics are analyzed by a numerical reverse leakage model, which includes both the image-force lowering and doping effects. We found that the reverse leakage current is near-ideal and dominated by Schottky barrier tunneling throughout the entire range of the surface electric field from 0.8 MV/cm to 3.4 MV/cm. The extracted barrier height from the reverse leakage model is consistent with the values extracted from the forward current–voltage and capacitance–voltage measurements. The practical maximum electric field, defined by the maximum allowable reverse leakage current levels, is calculated as a function of the barrier height. These results suggest that it is possible to approach the intrinsic breakdown electric field in β-Ga2O3 SBDs, as long as a sufficiently high barrier height (∼2.2 to 3 eV) is employed.

Surface states on (001) oriented halide vapor phase epitaxy (HVPE) grown β-Ga2O3 epilayers were explored through the determination of the Schottky barrier height (SBH) as a function of the metal work function using Cr, Cu, Ni, and Au Schottky barrier diodes. SBH is found to be nearly pinned between 1.2 and 1.35 eV in the HVPE grown epilayers. The position of the Fermi level pinning is closely matched with the energy level of the oxygen vacancy [VO(III)] state (EV + 3.57 eV) in the energy bandgap of β-Ga2O3, indicating that Fermi level pinning is due to oxygen vacancy type surface states on (001) oriented β-Ga2O3 epitaxial layers. The Fermi level is found to be relatively unpinned on the bulk β-Ga2O3 (001) substrate, suggesting the presence of lower density of oxygen vacancy states on its surface. Hence, the HVPE growth process was found to be responsible for the presence of oxygen vacancy states [VO(III)] in the epilayer. Moreover, this work highlights the role of these surface states in determining the SBH on β-Ga2O3 (001) epilayers and also explains the reason behind the scattered data of SBH values reported in the literature. In addition to these results, we also showed an increment in the built-in potential and the reduction of reverse leakage current for the epilayer with lower surface state density, which gives a direct evidence of the effect of surface states on the properties of β-Ga2O3 (001) Schottky barrier diodes.

This work presents the temperature-dependent forward conduction and reverse blocking characteristics of a high-voltage vertical Ga2O3 power rectifier from 300 K to 600 K. Vertical β-Ga2O3 Schottky barrier diodes (SBDs) were fabricated with a bevel-field-plated edge termination, where a beveled sidewall was implemented in both the mesa and the field plate oxide. The Schottky barrier height was found to increase from 1.2 eV to 1.3 eV as the temperature increases from 300 K to 600 K, indicating the existence of barrier height inhomogeneity. The net donor concentration in the drift region shows little dependence on the temperature. The reverse leakage current up to 500 V was found to be limited by both the thermionic-field electron injection at the Schottky contact and the electron hopping via the defect states in the depletion region. At 300–500 K, the leakage is first limited by the electron injection at low voltages and then by the hopping in depleted Ga2O3 at high voltages. At temperatures above 500 K, the thermionic field emission limits the device leakage over the entire voltage range up to 500 V. Compared to the state-of-the-art SiC and GaN SBDs when blocking a similar voltage, our vertical Ga2O3 SBDs are capable of operating at significantly higher temperatures and show a smaller leakage current increase with temperature. This shows the great potential of Ga2O3 SBDs for high-temperature and high-voltage power applications.

Mg diffusion is a common problem in GaN devices with p–n junctions. Although this impurity diffusion is reported to occur through threading dislocations (TDs), no direct evidence has yet been obtained. Therefore, we tried the direct observation of Mg diffusion by atom probe tomography (APT) analysis. The n-type drift layer of the fabricated p–n diode was exposed, and etch pits were formed on the drift layer to identify the TD position. The APT analysis around TDs was carried out by lifting out the drift layer around specific etch pits using a focused ion beam to include TDs. The relationship between the etch pit shape and the TD type was confirmed by cross-sectional scanning transmission electron microscopy observation. The APT analysis of two types of etch pits formed on the mixed dislocations was performed, and Mg diffusion was clearly observed through the mixed dislocations. In this work, we show direct evidence of Mg diffusion via mixed dislocations in GaN p–n diodes and its effect on reverse leakage current.

Oxidized iridium (IrOx) Schottky contacts (SCs) with excellent high temperature stability were fabricated on 2 ¯ 01 β-Ga2O3 single crystal substrates. These IrOx:β-Ga2O3 SCs were operated at temperatures from 24 to 350 °C with only a very small increase in reverse leakage current, while maintaining extremely high rectification ratios (at ±3 V) of more than 10 orders of magnitude at all temperatures, including 350 °C. This remarkable high temperature performance was due to their very high and thermally stable rectifying barriers that, after an initial heat-related improvement, were characterized by zero-bias effective barrier heights of 2.05 ± 0.02 eV and ideality factors of 1.05–1.10, which were almost unchanged by further repeated operation at 350 °C. The reverse leakage current density at 350 °C was only ∼2.3 × 10−9 A cm−2 (∼3.0 pA) at −3 V and ∼7.5 × 10−8 A cm−2 (∼100 pA) at −100 V. These IrOx:β-Ga2O3 SCs represent a significant improvement in high-temperature β-Ga2O3 SC performance, with considerable potential for the fabrication of high temperature β-Ga2O3 rectifying diodes, deep UV photodetectors, and metal-semiconductor field effect transistors.

CsPbBr3 quantum dots (QDs) were doped into a blend of poly(3-hexylthiophene) and indene-C60 bisadduct to fabricate bulk heterojunction polymer photodetectors. The addition of the QDs significantly increased the shunt resistance of the device, thereby suppressing the reverse leakage current and improving both the signal-to-noise ratio and the specific detectivity. The photoresponse and recovery time both decreased because of the enhanced built-in electric field and improved charge carrier mobility.CsPbBr3 quantum dots (QDs) were doped into a blend of poly(3-hexylthiophene) and indene-C60 bisadduct to fabricate bulk heterojunction polymer photodetectors. The addition of the QDs significantly increased the shunt resistance of the device, thereby suppressing the reverse leakage current and improving both the signal-to-noise ratio and the specific detectivity. The photoresponse and recovery time both decreased because of the enhanced built-in electric field and improved charge carrier mobility.

β-Ga2O3 vertical trench Schottky barrier diodes (SBDs) are realized, demonstrating superior reverse blocking characteristics than the co-fabricated regular SBDs. Taking advantage of the reduced surface field effect offered by the trench metal-insulator-semiconductor structure, the reverse leakage current in the trench SBDs is significantly suppressed. The devices have a higher breakdown voltage of 1232 V without optimized field management techniques, while having a specific on-resistance (Ron,sp) of 15 mΩ cm2. An ultra-low leakage current density of

Dislocations that cause a reverse leakage current in vertical p-n diodes on a GaN free-standing substrate were investigated. Under a high reverse bias, dot-like leakage spots were observed using an emission microscope. Subsequent cathodoluminescence (CL) observations revealed that the leakage spots coincided with part of the CL dark spots, indicating that some types of dislocation cause reverse leakage. When etch pits were formed on the dislocations by KOH etching, three sizes of etch pits were obtained (large, medium, and small). Among these etch pits, only the medium pits coincided with leakage spots. Additionally, transmission electron microscopy observations revealed that pure screw dislocations are present under the leakage spots. The results revealed that 1c pure screw dislocations are related to the reverse leakage in vertical p-n diodes.

β-Ga2O3 Schottky barrier diodes (SBDs) have been fabricated on a bulk (100) β-Ga2O3 substrate and tested as X-ray detectors in this study. The devices exhibited good rectification properties, such as a high rectification ratio and a close-to-unity ideality factor. A high photo-to-dark current ratio exceeding 800 was achieved for X-ray detection, which was mainly attributed to the low reverse leakage current in the β-Ga2O3 SBDs. Furthermore, transient response of the β-Ga2O3 X-ray detectors was investigated, and two different detection mechanisms, photovoltaic and photoconductive, were identified. The results imply the great potential of β-Ga2O3 based devices for X-ray detection.

In this work, we report on defect-free homogeneous behavior of Ni Schottky contacts patterned on surface treated n-GaN by photolithography with unity ideality factor, high temperature stability, and low reverse leakage. The barrier height (0.7 eV) and ideality factor (1.02) are found to be independent of temperature, indicating a highly homogeneous contact. The contacts are found to be stable with no significant change in ideality factor or leakage current up to an annealing temperature of 600 °C. Temperature dependence of the reverse leakage current shows no evidence for the existence of surface defects that would provide leakage paths, and the behavior was modeled by ATLAS simulations with an ideal homogeneous barrier of 0.7 eV. Consequently, the forward and reverse bias characteristics are explained by a common set of parameters. The surface treatment after the development and prior to metallization included an acid-based surface treatment. X-ray photoelectron spectroscopy (XPS) studies indicate that t...

High-performance thin-film silicon n–i–p diodes are fabricated at temperatures below 160°C using hot-wire chemical vapor deposition. The 0.01mm2 diodes have a forward current-density of near 1000A∕cm2 and a rectification ratio over 107 at ±2V. Use of microcrystalline silicon i and n layers results in higher current-density diodes than with amorphous silicon, primarily by lowering a barrier to carrier injection. A 30nm intrinsic Si buffer layer between the i and p layers is needed to reduce the reverse leakage current. Minimizing diode area increases forward current density by reducing the voltage drop across the external series resistances.

application/pdf, Anisotropy of the impact ionization coefficients of 4H silicon carbide is investigated by means of the avalanche breakdown behavior of p+n diodes on (0001) and (11[overline 2]0) 4H silicon carbide epitaxial wafers. The impact ionization coefficients are extracted from the avalanche breakdown voltages and the multiplication of a reverse leakage current, due to impact ionization of these p+n diodes. The breakdown voltage of a p+n diode on a (11[overline 2]0) wafer is 60% of that on a (0001) wafer, and the extracted impact ionization coefficients of 4H silicon carbide show large anisotropy. We have shown that the anisotropy of the impact ionization coefficients is related to the anisotropy of carrier heating and drift velocity, which are due to the highly anisotropic electronic structure of 4H silicon carbide.

We have used conductive atomic force microscopy (C–AFM) to investigate the forward and reverse bias current conduction of homo- and heteroepitaxial GaN-based films grown by molecular beam epitaxy. In the case of homoepitaxy, C–AFM shows enhanced current conduction at the centers of ∼30% of spiral hillocks, which are associated with screw dislocations. Local current–voltage spectra taken by C–AFM on and off such hillocks indicate Frenkel–Poole and field emission mechanisms, respectively, for low current levels in forward conduction. In the case of heteroepitaxial GaN films grown on sapphire, the correlation between conduction pathways and topography is more complex. We do observe, however, that films with more rectifying nominal Schottky behavior (less reverse leakage current) produce forward and reverse bias C–AFM images with strong asymmetry.

We fabricated pn diodes on the 4H–SiC(000-1) C and (11-20) face. The epitaxial growth of the n-type drift layer was carried out in chemical vapor deposition (CVD) reactor under the optimized conditions for each substrate. The pn junction was formed by Al+ ion implantation with multiple energy implantation (30–200 kV) at 600 °C subsequent annealing at 1600 °C for 5 min in Ar ambient. In the case of the diode on the (000-1) C face, we observed an abrupt avalanche breakdown, which is very similar to the case of the (0001) Si face, at the theoretical breakdown voltage (1150 V) calculated from the doping concentration and the thickness of the drift layer. This result means that there is no difference in the quality of the epitaxial layer between the (0001) Si and the (000-1) C face. On the other hand, a lower breakdown voltage (1200 V) than the theoretical value (1900 V) was observed in the case of the diode on the (11-20) face, and moreover, serious reverse leakage current was also observed. On the basis of t...

The thermal stability of Ni Schottky contacts on strained Al0.3Ga0.7N/GaN heterostructures and on n-type bulk GaN was investigated after various thermal stressings using capacitance–voltage and current–voltage characterization techniques. The reverse leakage current decreases after thermal treatment at up to 800 and 600 °C for Schottky contacts on the strained Al0.3Ga0.7N/GaN heterostructures and bulk n-GaN, respectively. Ni Schottky contacts on the heterostructure with 30-min thermal stressing at 700 °C exhibit lower reverse leakage current by more than three orders of magnitude lower than the control sample. However, decrease in two-dimensional electron gas sheet carrier concentration at the Al0.3Ga0.7N and GaN interface possibly due to interactions between Ni and AlGaN surface was observed with increase of stressing temperature and time. Ni Schottky contacts on bulk n-GaN layers degrade at lower annealing temperature and their rectifying property practically disappears after 700 °C annealing, while Al0...

We present a method of forming shallow p-doping on a 4H-SiC surface by depositing a thin Al layer (d = 5 nm) and then thermally annealing it at 1000 °C for 10 min. A secondary ion mass spectrometry analysis of the annealed Al/SiC sample reveals an Al concentration in excess of 1017 cm−3 up to a depth of d ≤ 250 nm. I–V measurements and CV characterizations of Ti-SiC Schottky barrier diodes (SBDs) fabricated on a n-type SiC epi-wafer indicate that the shallow Al doping increases the built-in potential of the junction and the barrier height by ΔVbi=0.51 eV and ΔϕB=0.26 eV, respectively. Assuming a rectangular doping profile, calculations of the built-in voltage shift and the Schottky barrier height indicate that partial dopant activation (activation ratio ∼2%) can induce the observed barrier height shift. The shallow doping method was then used to fabricate junction terminations in SBDs which increased the breakdown voltage and reduced the reverse leakage current. Technology CAD simulations of the SBD with ...

In a vertical GaN Schottky barrier diode, the free electron concentration n in the 6-μm-thick drift layer was found to greatly impact the diode reverse leakage current, which increased from 2.1 × 10−7 A to 3.9 × 10−4 A as n increased from 7.5 × 1014 cm−3 to 6.3 × 1015 cm−3 at a reverse bias of 100 V. By capping the drift layer with an ultrathin 5-nm graded AlGaN layer, reverse leakage was reduced by more than three orders of magnitude with the same n in the drift layer. We attribute this to the increased Schottky barrier height with the AlGaN at the surface. Meanwhile, the polarization field within the graded AlGaN effectively shortened the depletion depth, which led to the formation of tunneling current at a relatively small forward bias. The turn-on voltage in the vertical Schottky diodes was reduced from 0.77 V to 0.67 V—an advantage in reducing conduction loss in power switching applications.

We report on the fabrication of n-ZnO/p-AlGaN heterojunction light-emitting diodes on 6H-SiC substrates. Hydride vapor phase epitaxy was used to grow p-type AlGaN, while chemical vapor deposition was used to produce the n-type ZnO layers. Diode-like, rectifying I-V characteristics, with threshold voltage ~3.2V and low reverse leakage current ~10(-7)A, are observed at room temperature. Intense ultraviolet emission with a peak wavelength near 389 mn is observed when the diode is forward biased; this emission is found to be stable at temperatures up to 500K and shown to originate from recombination within the ZnO.

A thermally stable IrO2 Schottky contact on n-type 4H-SiC was achieved by annealing an Ir contact under O2 ambient. The IrO2 contact exhibited a high Schottky barrier height of 2.22 eV and low reverse leakage current. Little degradation in Schottky barrier height was observed even after annealing at 450 °C for 24 h under atmospheric air. The oxidation annealing transformed the Ir layer into IrO2, resulting in the increase in the work function of the contact layer. Simultaneously, Si atoms diffused out, leaving the Si vacancy below the contact. These played a role in forming a thermally stable Schottky contact with a high Schottky barrier height.

Using a photoelectrochemical method involving a He–Cd laser, Ga2O3 oxide layers were directly grown on n-type GaN. We demonstrated the performance of the resultant metal–oxide–semiconductor devices based on the grown Ga2O3 layer. An extremely low reverse leakage current of 200 pA was achieved when devices operated at −20 V. Furthermore, high forward and reverse breakdown electric fields of 2.80 MV/cm and 5.70 MV/cm, respectively, were obtained. Using a photoassisted current–voltage method, a low interface state density of 2.53×1011 cm−2 eV−1 was estimated. The varactor devices permit formation of inversion layers, so that they may be applied for the fabrication of metal–oxide–semiconductor field-effect transistors.

The effect of preannealing of AlGaN under an oxygen ambient on the improvement of the Schottky barrier height on an AlGaN/GaN heterostructure was studied using synchrotron radiation photoemission spectroscopy. The oxidation annealing increased the Schottky barrier height from 0.59 to 0.84 eV, and dramatically reduced the reverse leakage current. The group-III elements (Ga, Al) outdiffused to the surface to form group-III oxides during the annealing, leaving group-III vacancies behind. The surface Fermi level shifted to the energy levels of group-III vacancies, leading to the enhancement of Schottky properties of AlGaN.

KOH etch was investigated as a means to improve the I–V characteristics of Schottky diodes on n-type GaN grown by molecular-beam epitaxy on sapphire, or on hydride vapor phase epitaxy templates. Atomic force microscopy images and I–V characteristics are presented. After etching as-grown films in molten KOH, Schottky diodes on c-plane GaN had orders of magnitude reduction in reverse leakage current. The best devices had leakage currents less than 10−12 A (10−8 A/cm2) at −5 V, and ideality factors of 1.04. Measurements on several different sample structures indicate a correlation between surface roughness and saturation current, and an improvement in ideality factor when etched in KOH. Phosphoric acid was also investigated, but did not result in significant improvements in I–V characteristics.

We report thermally stable Ir Schottky contacts on AlGaN/GaN heterostructure. The Schottky barrier height was increased from 0.68 to 1.07 eV, and the reverse leakage current dramatically decreased after annealing at 500 °C under O2 ambient. No degradation in Schottky barrier height was observed after annealing at 500 °C for 24 h. The oxidation annealing caused predominant Ga outdiffusion to the surface, leading to the shift of surface Fermi level to the energy level of Ga vacancy. This played a role in forming the Schottky contact with large barrier height and excellent thermal stability.

Iridium oxide (IrO2) was used as the Schottky barrier materials of GaN metal–semiconductor–metal (MSM) ultraviolet photodetector. Annealing an Ir contact at 500 °C under O2 ambient, the reverse leakage current density at −5 V reduced by the four orders of magnitude, to ∼10−6 A/cm2. Simultaneously, Schottky barrier height and optical transmittance increased to 1.48 eV and 74.8% at 360 nm, respectively. The dramatic improvement originated from the formation of IrO2 by the annealing, resulting in the increase in the responsivity of the GaN MSM photodetector by one order of magnitude, in comparison with the photodetector with Pt Schottky contact.

4H-SiC Schottky rectifiers with dielectric overlap edge termination were exposed to 40 MeV protons at fluences from 5×107–5×109 cm−2. The reverse breakdown voltage decreased from ∼500 V in unirradiated devices to ∼−450 V after the highest proton dose. The reverse leakage current at −250 V was approximately doubled under these conditions. The forward current at −2 V decreased by ∼1% (fluence of 5×107 cm−2) to ∼42% (fluence of 5×109 cm−2), while the current at lower biases was increased due to the introduction of defect centers. The ideality factor, on-state resistance, and forward turn-on voltage showed modest increases for fluences of ⩽5×108 cm−2, but were more strongly affected (increase of 40%–75%) at the highest dose employed.

GaN films were grown on sapphire and SiC substrates. The crystal qualities of GaN films were investigated by photoluminescence, atomic force microscopy, and electron-beam-induced current measurements, etc. It was found that the crystal quality of GaN on SiC is better than the one on sapphire. Ni/Au Schottky contacts were formed on the both samples. The electronic characteristics were obtained by current–voltage and capacitance–voltage measurements. Schottky diodes on sapphire substrate show breakdown voltage of −80 V. While for SiC substrate, the strong breakdown was not observed even at −100 V. The reverse leakage current of diodes based on SiC is over three orders of magnitude lower than that of sapphire substrate when the reverse voltage is above 50 V, which is due to the presence of low dislocation density and high thermal conductivity.

Conduction mechanisms for the off-state leakage in Schottky barrier thin-film transistor were explored. It was found that the field-emission process dominates the leakage conduction of the device with the conventional structure as the field strength in the drain junction becomes high, and results in the strong gate-induced drain leakage (GIDL) like phenomenon. In contrast, for the device with a field-induced-drain structure, the high-field region is pulled away from the silicided drain. As a result, the field-emission conduction is eliminated, so the GIDL-like leakage current is effectively suppressed.

The results of the sulfur treatment of multiple-quantum-well (MQW) light-emitting diodes (LEDs) with (NH4)2S and (NH4)2S+t-C4H9OH solutions prior to the deposition of a light-transmitting p-electrode metal are presented. The room-temperature I–V curves showed that the forward voltages of MQW LEDs treated with the two sulfur solutions decrease by 0.12 and 0.35 V at 20 mA, respectively, compared to the untreated MQW LED, as the result of an improvement in p-Ohmic contact characteristics. The relative light-output power and external quantum efficiency of MQW LEDs increased by a factor of 1.28 for the (NH4)2S treated sample and 2.23 for the (NH4)2S+t-C4H9OH treated sample compared to the untreated sample. In addition, the reverse leakage current characteristic of MQW LEDs was reduced as a result of sulfur treatment. This can be attributed to the passivation of surface and sidewall damages formed after the dry-etching process for a reliable pattern transfer. The present results indicate that the sulfur treatme...

We report on a transparent Schottky-barrier ultraviolet detector on GaN layers over sapphire substrates. Using SiO2 surface passivation, reverse leakage currents were reduced to a value as low as 1 pA at 5 V reverse bias for 200 μm diameter device. The device exhibits a high internal gain, about 50, at low forward biases. The response time (about 15 ns) is RC limited, even in the internal gain regime. A record low level of the noise spectral density, 5×10−23 A2/Hz, was measured at 10 Hz. We attribute this low noise level to the reduced reverse leakage current.

An In0.5(Al0.66Ga0.34)0.5P/GaAs heterostructure field-effect transistor has been fabricated by metal-organic chemical vapor deposition. A turn-on voltage as high as 3.2 V along with an extremely low gate reverse leakage current of 69 μA/mm at VGD=−40 V are achieved. In addition, it is found that the device can be operated with gate voltage up to 1.5 V without significant drain current compression. These characteristics are attributed to the use of high Schottky barrier height, high band gap of In0.5(Al0.66Ga0.34)0.5P Schottky layer, and to the large conduction-band discontinuity at the In0.5(Al0.66Ga0.34)0.5P/GaAs heterojunction.

Ge1−xCx/Si heterostructure photodiodes with nominal carbon percentages (0⩽x⩽0.02), which exceed the solubility limit, were grown by solid source molecular beam epitaxy on n-type (100) Si substrates. The p-Ge1−xCx/n-Si photodiodes were fabricated and tested. The p-Ge1−xCx/n-Si junction exhibits diode rectification with a reverse saturation current of about 10 pA/μm2 at −1 V and high reverse breakdown voltage, up to −80 V. A significant reduction in diode reverse leakage current was observed by adding C to Ge, but these effects saturated with more C. Photoresponsivity was observed from these Si-based p-Ge1−xCx/n-Si photodiodes at a wavelength of ⩾1.3 μm, compatible with fiber optic wavelengths. External quantum efficiency of these thin surface-normal photodetectors was measured up to 2.2%, which decreased as the carbon percentage was increased.

A dual-material structure of lattice-matched GaInP on GaAs has a calculated figure of merit which is approximately 60 times better than Si and 5 times better than GaAs. In this work, the theoretical performance of the GaInP/GaAs structure is presented and experimental data for Ni on GaInP/GaAs Schottky rectifiers is presented. The Ni on GaInP/GaAs Schottky rectifiers have a breakdown voltage of ∼80 V and low reverse leakage current. Comparable Ni on GaAs Schottky rectifiers have a breakdown voltage of ∼20 V and significantly higher reverse leakage current. The GaInP/GaAs rectifiers’ forward characteristics have a current–voltage extracted φBn of 1.0 eV with an ideality factor of 1.06. This dual-material structure of GaInP/GaAs appears to be a promising candidate for improving power device performance.

Reactively sputtered AlN is shown by electrical characterization of Pt/Au Schottky diodes to be an effect encapsulant for GaN annealed at 1100 °C. Schottky diodes formed on GaN encapsulated with AlN during the anneal had low reverse leakage currents with breakdown voltages in excess of 40 V. In contrast, samples annealed without the AlN layer had 3–4 orders‐of‐magnitude higher reverse leakage currents. Atomic force microscopy images of as‐grown and annealed samples also demonstrate an increase in surface roughness and a change in morphology of the uncapped samples following annealing. Auger electron spectroscopy supports the hypothesis that the AlN encapsulant is reducing N loss from the GaN substrate. N loss in the uncapped samples is expected to create an n+‐region at the surface that accounts for the high reverse leakage current and improved Ohmic behavior for the uncapped samples. The use of AlN encapsulation will enable the realization of all ion implanted GaN metal semiconductor field effect transis...

The reverse leakage current in strained multiple quantum well (MQW) p‐i‐n structures has been measured for a range of different dimensions and strain. The magnitude of the leakage current is found to be dependent on the average strain of the MQW, the total MQW thickness and the thickness of the capping layer. Plan view transmission electron microscopy shows that misfit dislocation arrays form primarily at the upper and lower MQW interfaces and the total density of these determine the leakage current.

Improved Al/InP Schottky barriers are formed on n‐InP by using coimplantation of Be/P. The doped surface layer (Be) helps in retarding the surface fields, resulting in larger Schottky barrier heights. The addition of phosphorus prevents excessive P loss and enhances the percentage of Be activation. A Schottky barrier height as high as 0.64 eV has been obtained, as compared to 0.55 eV for diodes without P implantation. The ideality factor is found to be very close to unity (≊1.08). The reverse leakage current density is reduced by almost four orders of magnitude. To demonstrate the versatility of our process, the same technique is applied to p‐InP samples. As expected, the barrier height is reduced by almost 0.5 eV. Furthermore, the sum of the two Schottky barrier heights also matches closely with the theoretical value of energy band gap for InP.

High performance titanium nitride sub-100 nm rectifying contact, deposited by sputtering on AlGaN/GaN high electron mobility transistors, shows a reverse leakage current as low as 38 pA/mm at VGS = -40 V and a Schottky barrier height of 0.95 eV. Based on structural characterization and 3D simulations, it is found that the polarization gradient induced by the gate metallization forms a P-type pseudo-doping region under the gate between the tensile surface and the compressively strained bulk AlGaN barrier layer. The strain induced by the gate metallization can compensate for the piezoelectric component. As a result, the gate contact can operate at temperatures as high as 700 °C and can withstand a large reverse bias of up to -100 V, which is interesting for high-performance transistors dedicated to power applications.

Highly rectifying heterojunctions of n-type nanocrystalline diamond (NCD) films to p-type 4H-SiC substrates are fabricated to develop p-n junction diodes operable at high temperatures. In reverse bias condition, a potential barrier for holes at the interface prevents the injection of reverse leakage current from the NCD into the SiC and achieves the high rectification ratios of the order of 10{sup 7} at room temperature and 10{sup 4} even at 570 K. The mechanism of the forward current injection is described with the upward shift of the defect energy levels in the NCD to the conduction band of the SiC by forward biasing. The forward current shows different behavior from typical SiC Schottky diodes at high temperatures.

Ni/GaN Schottky barrier diodes were irradiated with 200 MeV Ag ions up to fluence of 1 × 1011 ions/cm2 at the substrate temperature of 80 K. Post-irradiation current-voltage measurements showed that the ideality factor, n increased and the reverse leakage current, IR decreased with increase in fluence. But Schottky barrier height, ϕb increased only marginally with increase in ion fluence. In situ resistivity measurements showed orders of magnitude increase in resistivity of GaN epitaxial film with irradiation fluence. Cross-sectional transmission electron microscopy images revealed the presence of defect clusters in bulk GaN after irradiation.

We report here the successful fabrication of a planar, low dark current, and high sensitivity In0.4Ga0.6As p‐i‐n photodiode fabricated on a semi‐insulating GaAs substrate with the aid of a multistage strain‐relief buffer system. Without using surface passivation and anti‐reflection coatings, the detector has a quantum efficiency of 42% and a peak responsivity of 0.45 A/W at 1.3 μm wavelength. The reverse leakage current for the mesa‐etched photodiode with an active area of 2×10−4 cm2 is 5×10−9 A at −5 V, and the breakdown voltage exceeds 25 V.

Light‐emitting diodes (LEDs) have been fabricated on GaAs‐on‐Si substrates grown by a hybrid method which combines molecular beam epitaxy (MBE) and liquid phase epitaxy. The LEDs had a low reverse leakage current and high stability of light intensity for an aging operation compared with MBE‐grown LEDs. These results are attributed to a higher crystallinity in the hybrid‐grown GaAs layers on Si substrates.