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Thick (23 µm) films of κ-Ga2O3 were grown by Halide Vapor Phase Epitaxy (HVPE) on GaN/sapphire templates at 630 °C. X-ray analysis confirmed the formation of single-phase κ-Ga2O3 with half-widths of the high-resolution x-ray diffraction (004), (006), and (008) symmetric reflections of 4.5 arc min and asymmetric (027) reflection of 14 arc min. Orthorhombic κ-Ga2O3 polymorph formation was confirmed from analysis of the Kikuchi diffraction pattern in electron backscattering diffraction. Secondary electron imaging indicated a reasonably flat surface morphology with a few (area density ∼103 cm−2) approximately circular (diameter ∼50–100 µm) uncoalesced regions, containing κ-Ga2O3 columns with in-plane dimensions and a height of about 10 µm. Micro-cathodoluminescence (MCL) spectra showed a wide 2–3.5 eV band that could be deconvoluted into narrower bands peaked at 2.59, 2.66, 2.86, and 3.12 eV. Ni Schottky diodes prepared on the films showed good rectification but a high series resistance. The films had a thin near-surface region dominated by Ec − 0.7 eV deep centers and a deeper region (∼2 µm from the surface) dominated by shallow donors with concentrations of ≤1016 cm−3. Photocurrent and photocapacitance spectra showed the presence of deep compensating acceptors with optical ionization energies of ∼1.35 and 2.3 eV, the latter being close to the energy of one of the MCL bands. Deep level transient spectroscopy revealed deep traps with energies near 0.3, 0.6, 0.7, 0.8, and 1 eV from the conduction band edge. The results show the potential of HVPE to grow very thick κ-Ga2O3 on GaN/sapphire templates. [ABSTRACT FROM AUTHOR]

Ni/GaN Schottky diode radiation detectors were fabricated on 3-μm-thick unintentionally doped n-GaN films grown by molecular beam epitaxy (MBE) and metal organic chemical vapor deposition (MOCVD) and on 12-μm-thick undoped n-GaN layers prepared by epitaxial lateral overgrowth (ELOG). The reverse current of all detector structures was <10-9 A for bias voltages necessary for detector operation, with the level of background donor doping of <1015 cm-3. With this doping level the space charge region of the Schottky diode could be extended to the entire thickness of the films. The charge collection efficiency of the detectors was close to 100% for MOCVD and ELOG detectors for α-particles with range comparable to the thickness of the layer. Electrical properties and deep trap spectra were also studied. The collection efficiency decreased when the concentra-tion of deep electron traps, particularly Ec-0.6 eV traps, increased in MBE grown films. [ABSTRACT FROM AUTHOR]

The transport properties of as-deposited and rapid thermal annealed phosphorus-doped ZnO films grown by pulsed laser deposition are reported. As-grown ZnO:P samples showed n-type characteristics, presumably due to the formation of antisite PZn defects. Rapid thermal annealing yielded a carrier-type conversion from n- to p-type for the ZnO:P films grown at ∼700 °C; samples grown at substantially lower or higher temperatures tended to remain n-type even after the thermal annealing process. The properties and behavior of the n-to-p conversion are most consistent with the formation of PZn-2VZn as the active acceptor state. Variable magnetic field Hall measurements confirmed the p-type behavior. Phosphorus doping concentrations in the range of 0.5-1.0 at. % were considered, with evidence for P segregation in the higher phosphorus concentrations. [ABSTRACT FROM AUTHOR]

The magnetic and transport properties of Mn-doped ZnO thin films co-doped with P are examined. Superconducting quantum interference device magnetometry measurements indicate that the films are ferromagnetic with an inverse correlation between magnetization and electron density as controlled by P doping. In particular, under conditions where the acceptor dopants are activated leading to a decrease in free-electron density, magnetization is enhanced. The result is consistent with hole-mediated ferromagnetism in Mn-doped ZnO, in which bound acceptors mediate the ferromagnetic ordering. Increasing the electron density decreases the acceptor concentration, thus quenching the ferromagnetic exchange. This result is important in understanding ferromagnetism in transition metal doped semiconductors for spintronic devices. [ABSTRACT FROM AUTHOR]

The properties of ZnO films grown by molecular-beam epitaxy are reported. The primary focus was on understanding the origin of deep-level luminescence. A shift in deep-level emission from green to yellow is observed with reduced Zn pressure during the growth. Photoluminescence and Hall measurements were employed to study correlations between deep-level/near-band-edge emission and carrier density. With these results, we suggest that the green emission is related to donor-deep acceptor (Zn vacancy VZn-) and the yellow to donor-deep acceptor (oxygen vacancy, Oi-). [ABSTRACT FROM AUTHOR]

The magnetic and transport properties of Mn-doped ZnO thin films codoped with Sn are examined. Superconducting quantum interference device magnetometry measurements indicate that the films are ferromagnetic with an inverse correlation between magnetization and electron density as controlled by Sn doping. Magnetism in low free-electron density material is consistent with the bound magnetic polaron model, in which bound acceptors mediate the ferromagnetic ordering. Increasing the electron density decreases the acceptor concentration, thus quenching the ferromagnetic exchange. This result is important in understanding ferromagnetism in transition-metal-doped semiconductors for spintronic devices. [ABSTRACT FROM AUTHOR]

We report an optical spectroscopic method to monitor NiAs-type MnAs (α-MnAs) nanocrystals in (Ga,Mn)As diluted magnetic semiconductors. We utilize Mn ion implantation of low temperature (LT) GaAs epitaxial thin films followed by rapid thermal annealing (RTA) to yield embedded ferromagnetic α-MnAs nanoclusters in a GaAs:Mn matrix. As-implanted samples are paramagnetic and become ferromagnetic with Curie temperature of ∼320 K after RTA at 750 °C. No peaks of potential secondary phases could be observed in x-ray diffraction measurements. However, in optical spectra, the annealed samples show resonant absorption at 0.9 eV photon energy, due to resonant surface plasma oscillation of spherical metallic phases embedded in LT GaAs. Since the absorption peak position in the photon energy has a direct relation to the value of the plasma frequency of metallic inclusions, the metallic clusters in LT GaAs are identified as α-MnAs nanocrystals by comparing them with simulations based on Maxwell–Garnett theory. We suggest that this optical method can be applied to various granular systems and diluted magnetic semiconductors as a nondestructive way to detect and quantify metallic nanoclusters. © 2004 American Institute of Physics. [ABSTRACT FROM AUTHOR]

The electrical properties, deep level spectra, and microcathodoluminescence (MCL) spectra of p-GaN films implanted with 100 keV protons are reported. Measurable decreases of the MCL intensity began for doses as low as 10[sup 12] cm[sup -2], while measurable decreases of the hole concentration started for doses of 10[sup 13] cm[sup -2]. The main deep traps introduced by protons had activation energies of 0.3, 0.6, and 0.9 eV. The 0.3 and 0.9 eV traps are located in the lower half of the band gap and determine the temperature dependence of the forward current in heavily proton implanted Schottky diodes. © 2003 American Institute of Physics. [ABSTRACT FROM AUTHOR]

The diode ideality factor, reverse breakdown voltage, and forward current characteristic were used to measure the effect on electric performance of GaAs rectifiers deposited with thin films of SiN[sub x]. Over a broad range of deposition conditions there were minimal changes (<10%) in breakdown voltage and the cause was hydrogen passivation of Si dopants in the GaAs. Ion-induced damage did not appear to play a significant role in the results. The ideality factors and forward leakage currents were essentially unchanged by the SiN[sub x] deposition indicating that the plasma exposure did not create defects states around the periphery of the Schottky contact. © 2001 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Presents a study which investigated tungsten thin films on n-InP layers for potential use as a refractory ohmic contact for self-aligned In-based etched mesa buried heterostructures laser devices. Experimental procedure; Results and discussion; Conclusions.

Discusses a study on rapid-thermal low pressure metalorganic chemical vapor deposited titanium-nitrogen films on indium-phosphate influenced by a combined reactive chemistry of ammonia gas and tetrakis titanium liquid precursors. Process kinetics; Chemical composition; Microstructures.

Presents a study in which titanium nitride thin films were deposited onto indium phosphide by means of rapid-thermal-low-pressure-chemical-vapor-deposition technique, using the tetrakis dimethylamido titanium Ti(NMe[sub2])[sub4] or DMATi complex as the precursor. Range of the film resistivity and stress; Deposition kinetics and uniformity of titanium nitride; Details on film stoichiometry and impurities incorporation.

Presents a study which investigated WSi[subx] thin films deposited on indium phosphide substrates for possible use as refractory ohmic contact materials for self-aligned laser devices. Microstructure and mechanical properties of WSi[subx] metallizations sputter deposited on indium phosphide; Techniques used to characterize the WSi[subx]/indium structures; Evaluation of the WSi[subx] layers for dry etching performance.

Carrier removal rates and deep trap spectra were measured in neutron irradiated n-GaN samples grown by metalorganic chemical vapor deposition (MOCVD), hydride vapor phase epitaxy (HVPE, and epitaxial lateral overgrowth (ELOG). The carrier removal rates were found to significantly increase with donor doping and to decrease in the sequence MOCVD/ ELOG/ HVPE. The most prominent traps created by irradiation were quasi-holc traps with energy 0.6-0.7 eV and electron traps with energy 0.45 eV. The former were associated with disordered regions in GaN and determine the carrier removal rate in undoped films. The latter were attributed to radiation defect complexes with shallow donors. [ABSTRACT FROM AUTHOR]

The authors investigated the effect of SiOx passivation layers on the bias stability of bottom gate amorphous (α-) InGaZnO4 thin film transistors (TFTs) fabricated on glass substrates. The use of rapid thermal annealing for unpassivated TFTs in air improved the device performance, showing larger drain current and field effect mobility compared to the as-fabricated TFTs. Threshold voltage (VTH) and subthreshold gate-voltage swing (S) for both unpassivated and passivated devices were found to be nearly independent of the low-gate-voltage stress (5 V), but both were strongly affected under a relatively high-voltage stress (>10 V). The positive VTH and S shifts after constant gate voltage stress (+20 V) of 1000 s were 1.8 V and 0.72 V decade-1 for the unpassivated devices and 1 V and 0.42 V decade-1 for the passivated devices, respectively. These results demonstrate that the SiOx passivation layer significantly reduced the shift in TFT’s characteristics. [ABSTRACT FROM AUTHOR]

Wide band gap semiconductors such as GaN and ZnO have continued to be at the forefront of spintronics research due to the demonstration of room-temperature ferromagnetism in these materials. A goal of this research is the fabrication of a spintronic device that may provide easy incorporation into existing GaN and ZnO technologies, higher integration density, and less power consumption that its electronic counterparts while achieving similar speeds. The progression of the ferromagnetic metals incorporated into GaN has moved from transition metals to rare earth metals such as the lanthanides. The properties of transition metal-doped ZnO thin films for the two most studied transition metal dopants, namely Mn and Co, are also discussed in this review. [ABSTRACT FROM AUTHOR]

The performance of amorphous InGaZnO4 thin film transistors with three different gate dielectrics (SiO2, SiON, and SiNx) is reported. The gate dielectric films were prepared by plasma enhanced chemical vapor deposition with SiH4, N2O, and NH3 gases at 250 °C. Current-voltage (C-V) and refractive index characterization showed that different film compositions were achieved when changing the flow rate of N2O in the precursor gas mixture. The use of SiNx films reduced the interfacial roughness of the channel/gate dielectric by a factor of 2.3 compared to SiO2. This results in an improvement of saturation mobility of the thin film transistors (TFTs) by a similar factor. An enhancement of subthreshold gate-voltage swing and drain current on-to-off ratio for TFTs with SiNx was also attributed to the reduction of the trap density at the channel/gate-dielectric interface. [ABSTRACT FROM AUTHOR]

Nonpolar a-GaN films were grown by hydride vapor phase epitaxy on r-sapphire. As the thickness of the grown films was increased from 50 to over 250 μm, the width of the double-crystal rocking curve for the (11–20) reflection decreased from 2000 to 500 arc sec, indicating a strong decrease in the dislocation density. Microcathodoluminescence mapping of the thick films suggests that the dislocation density is ∼102 cm-2, which is more than two orders of magnitude lower than for thin films. The authors also observe a corresponding decrease in the density of residual donors from 1020 to 1018 cm-3, with respective mobility increase from (10–20) to 150 cm2/V s. The luminescence spectra of the thin films show the presence of intense defect bands attributed in literature to stacking faults. These bands are very strongly suppressed in thick films, which also show about an order of magnitude higher band edge luminescence intensity. [ABSTRACT FROM AUTHOR]

The effects of the layer thickness and of Si doping on the dislocation type and density, electron concentration, and deep trap spectra were studied for epitaxially laterally overgrown (ELOG) GaN films with the ELOG region thickness varying from 6 to 12 μm. Electron beam induced current imaging shows that for the thickest layers, the major part of the threading dislocations are filtered out while for thinner films they bend, but do not go out of play. The concentration of residual donors and major electron traps is found to decrease with increasing the film thickness. Si doping suppresses the concentration of the main electron trap with activation energy of 0.6 eV and enhances the concentration of the main hole trap at Ev+0.85 eV. [ABSTRACT FROM AUTHOR]

Capacitance-voltage (C-V), capacitance-frequency (C-f), admittance spectroscopy, deep trap spectra, and far infrared reflectance measurements were performed on undoped and N-doped ZnO films deposited on sapphire by molecular beam epitaxy. The results show existence of a heavily doped n+ layer near the interface with the substrate. The presence of these layers explains the large difference between the electron concentrations measured in the films by Hall effect and C-V profiling or calculated from the plasma minimum frequency in reflectance. C-V data obtained at low temperatures show a prominent persistent photocapacitance in the films. Admittance spectra were dominated by electron traps with ionization level EC-0.3 eV commonly observed in ZnO crystals grown by all techniques. [ABSTRACT FROM AUTHOR]

The properties of phosphorus-doped (Zn,Mg)O polycrystalline and epitaxial thin films are described. The as-deposited (Zn,Mg)O:P films are n type with high electron carrier density. High resistivity is induced in the films with moderate temperature annealing, which is consistent with suppression of the donor state and activation of the deep acceptor. The resistivity of the as-deposited and annealed film is an order of magnitude higher than similar samples with no Mg, consistent with a shift in the conduction band edge relative to the defect-related donor state. The capacitance-voltage characteristics of annealed metal]insulator/P-doped (Zn,Mg)O structures in which the (Zn,Mg)O is polycrystalline exhibit p-type polarity. In addition, multiple polycrystalline devices comprising n-type ZnO/P-doped (Zn,Mg)O thin-film junctions display asymmetric I-V characteristics that are consistent with the formation of a p-n junction at the interface, although the ideality factor is anomalously high. [ABSTRACT FROM AUTHOR]

Electrical and optical properties of p-AlGaN films grown by metalorganic chemical vapour deposition and implanted with high doses (3 × 1016 cm-2) of 250 keV Mn and Cr ions are reported. Schottky diodes prepared on such implanted films after annealing at 700 °C show a strongly increased reverse leakage current and increased series resistance in the forward direction due to residual radiation damage related defects. The density of these defects was considerably higher for the Mn-implanted diodes which correlated with the higher expected radiation damage due to higher ion mass of Mn compared with Cr. Deep level measurements revealed the formation of hole traps with levels near Ev + 0.4 eV and Ev + 1 eV. Optical absorption measurements indicated the presence of two major defect bands at about 1.5–1.7 eV and 2.25–2.35 eV. The results are compared with earlier measurements on Cr- and Mn-implanted p-GaN films and on proton-implanted p-AlGaN films. [ABSTRACT FROM AUTHOR]

We investigated the transfer characteristics and the gate-bias stability of amorphous indium-gallium-zinc oxide thin-film transistors when the channel layer was exposed to hydrogen, oxygen, air, or vacuum at room temperature during measurements. The threshold voltage and the drain current were changed by the ambient atmospheres. The threshold voltage shift (ΔVth) under gate-bias stress was faster in hydrogen than in oxygen and vacuum. It is suggested that hydrogen exposure degrades the gate-bias stress stability due to surface accumulation layer creation. The characteristic trapping times, τ, in H2, O2, air, and vacuum were 5×103, 1.5×104, 2×104, and 6.3×104 s, respectively. [ABSTRACT FROM AUTHOR]

We have fabricated bottom-gate amorphous (α-) indium-gallium-zinc-oxide (InGaZnO4) thin film transistors (TFTs) on both paper and glass substrates at low processing temperature (≤100 °C). As a water and solvent barrier layer, cyclotene (BCB 3022–35 from Dow Chemical) was spin-coated on the entire paper substrate. TFTs on the paper substrates exhibited saturation mobility (μsat) of 1.2 cm2 V-1 s-1, threshold voltage (VTH) of 1.9 V, subthreshold gate-voltage swing (S) of 0.65 V decade-1, and drain current on-to-off ratio (ION/IOFF) of ∼104. These values were only slightly inferior to those obtained from devices on glass substrates (μsat∼2.1 cm2 V-1 s-1, VTH∼0 V, S∼0.74 V decade-1, and ION/IOFF=105–106). The uneven surface of the paper sheet led to relatively poor contact resistance between source-drain electrodes and channel layer. The ability to achieve InGaZnO TFTs on cyclotene-coated paper substrates demonstrates the enormous potential for applications such as low-cost and large area electronics. [ABSTRACT FROM AUTHOR]

AlGaN/GaN high electron mobility transistors (HEMTs) with a polarized polyvinylidene difluoride (PVDF) film coated on the gate area exhibited significant changes in channel conductance upon exposure to different ambient pressures. The PVDF thin film was deposited on the gate region with an ink-jet plotter. Next, the PDVF film was polarized with an electrode located 2 mm above the PVDF film at a bias voltage of 10 kV and 70 °C. Variations in ambient pressure induced changes in the charge in the polarized PVDF, leading to a change in surface charges on the gate region of the HEMT. Changes in the gate charge were amplified through the modulation of the drain current in the HEMT. By reversing the polarity of the polarized PVDF film, the drain current dependence on the pressure could be reversed. Our results indicate that HEMTs have potential for use as pressure sensors. [ABSTRACT FROM AUTHOR]

Thin-film transistors (TFTs) based on amorphous indium gallium zinc oxide (a-IGZO) were fabricated by radio-frequency magnetron sputtering on glass substrates. The TFT device structure was a bottom-gate type, consisting of indium zinc oxide and HfO, as electrodes (gate, source, and drain) and gate dielectric, respectively. The resistivity of the a-IGZO channel layer was ~1 Ω cm. TFTs with a 6 µm gate length and 100 µm gate width displayed a saturation mobility of ~7.2 cm² V-1 s-1, a threshold voltage of 0.44 V, a drain current on-off ratio of ~105, and subthreshold gate-voltage swing of ~0.25 V decade-1. After 1000 h aging time at room temperature, the saturation mobility remained almost constant while the threshold voltage shift was as small as 460 mV. The IGZO TETs based on HfO2 gate dielectrics sputtered near room temperature were found to be good candidates for applications on organic flexible substrates. [ABSTRACT FROM AUTHOR]

Ti(200 Å)/Au(800 Å) Ohmic contacts to n-type amorphous indium zinc oxide (IZO) films with carrier concentrations of (1×1015)–(5×1020) cm-3 showed as-deposited specific contact resistances in the range of (3×10-1)–(1×10-4) Ω cm2. Postgrowth annealing from 200 to 500 °C resulted in significant improvement in contact resistances due to increase of the carrier concentration in the near surface region of IZO layer, which can be attributed to the formation of Ti–O alloy phases that induce oxygen vacancies in the IZO. After annealing at 500 °C, the lowest contact resistance of 8×10-6 Ω cm2 was achieved in the sample with carrier concentration of 5×1020 cm-3. Temperature dependent measurement showed that tunneling was dominant transport mechanism in the contacts on the most highly doped films (n∼5×1020 cm-3) and thermionic emission on the most lightly doped films (n∼1×1015 cm-3). [ABSTRACT FROM AUTHOR]

Depletion-mode indium zinc oxide (IZO) channel thin film transistors were fabricated on glass substrates from layers deposited at room temperature using rf magnetron sputtering. The threshold voltage was in the range from -5.5 to -6.5 V depending on gate dielectric (SiO2) thickness and the drain current on-to-off ratio was ∼105. The maximum field effect mobility in the channel was ∼4.5 cm2 V-1 s-1, lower than the Hall mobility of ∼17 cm2 V-1 s-1 in the same layers, suggesting a strong influence of scattering due to trapped charges at the SiO2-IZO interface. The low deposition and processing temperatures make these devices suitable for applications requiring flexible substrates. [ABSTRACT FROM AUTHOR]

Deep ultraviolet emission from gadolinium (Gd)-implanted AlN thin films has been observed using photoluminescence (PL) spectroscopy. The AlN epilayers were ion implanted with Gd to a total dose of ∼6×1014 cm-2. Using the output at 197 nm from a quadrupled Ti:sapphire laser, narrow PL emission was observed at 318 nm, characteristic of the trivalent Gd ion. A broader emission band, also centered at 318 nm, was measured with excitation at 263 nm. The PL emission intensity decreased by less than a factor of 3 over the sample temperature range of 10–300 K and decay transients were of the order of nanoseconds. [ABSTRACT FROM AUTHOR]

Thin films of scandium oxide were epitaxially deposited on GaN via molecular beam epitaxy using elemental Sc and an oxygen plasma. After growth, the Sc2O3 films were annealed at a temperature of 800 °C for 5 min in the growth chamber. The structural quality of Sc2O3 films, before and after annealing, was characterized using high-resolution x-ray diffraction, atomic force microscopy (AFM), and high-resolution transmission electron microscopy (HRTEM). AFM of the films revealed smooth surfaces with 0.38 nm root mean square roughness and show evidence of step-flow growth. The rocking curve and reflectivity scans of the films reveal that the Sc2O3/GaN interface is abrupt and that it remains so after annealing. Pole figure and grazing incidence θ-2θ measurements show that the films are very textured along the c axis of the GaN substrate. HRTEM produced lattice images of the Sc2O3/GaN interface illustrating the single crystal growth of the Sc2O3 films on the GaN. [ABSTRACT FROM AUTHOR]

A comparison is made of the sensitivities for detecting hydrogen with Pt-coated single ZnO nanorods and thin films of various thicknesses (20–350 nm). The Pt-coated single nanorods show a current response of approximately a factor of 3 larger at room temperature upon exposure to 500 ppm H2 in N2 than the thin films of ZnO. The power consumption with both types of sensors can be very small (in the nW range) when using discontinuous coatings of Pt. Once the Pt coating becomes continuous, the current required to operate the sensors increases to the μW range. The optimum ZnO thin film thickness under our conditions was between 40–170 nm, with the hydrogen sensitivity falling off outside this range. The nanorod sensors show a slower recovery in air after hydrogen exposure than the thin films, but exhibit a faster response to hydrogen, consistent with the notion that the former adsorb relatively more hydrogen on their surface. Both ZnO thin and nanorods cannot detect oxygen. [ABSTRACT FROM AUTHOR]

The Schottky barrier height of Pt contacts on n-type (n∼1016 cm-3) thin film ZnO deposited by pulsed laser deposition was obtained from current–voltage measurements as a function of temperature. The resulting values ranged from 0.61±0.04 eV at 25 °C to 0.46±0.06 eV at 100 °C with saturation current densities of 1.5×10-4 A cm-2 (25 °C) to 6.0×10-2 A cm-2 (100 °C), respectively. The reverse current magnitude was larger than predicted by thermionic emission alone. The measured barrier height for Pt on ZnO is similar to the value reported for both Au and Ag rectifying contacts on this material. © 2004 American Institute of Physics. [ABSTRACT FROM AUTHOR]

We observed superparamagnetism in Co-ion-implanted anatase TiO[sub 2] thin films on SrTiO[sub 3] (001) substrates. After postannealing under oxygen pressure of 1.0×10[sup -6] Torr, the blocking temperature increased with increasing annealing temperature. Eventually, the 600 °C-annealed sample became ferromagnetic at room temperature. These phenomena can be explained by the formation of Co (or ferromagnetic Co compound) particles and their growth during postannealing, as directly observed with transmission electron microscopy. High oxygen pressure during annealing reduced the size of the clusters and saturation magnetization moment, which indicates that cobalt clustering should be the main cause of the room-temperature ferromagnetism in the Co-ion-implanted films. © 2003 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Interdevice isolation currents in mesa-isolated AlGaN/GaN high-electron-mobility transistors are found to exhibit thermally activated behavior, with an activation energy of ∼1.5 eV. This value is largely independent of surface cleaning processes or the type of passivation film (SiN[sub X], Sc[sub 2]O[sub 3], MgO) used to reduce the current collapse phenomena in the devices. However, the magnitude of the isolation current is a strong function of the surface treatment employed. The lowest isolation currents for conditions under which current collapse is mitigated are obtained using Sc[sub 2]O[sub 3] passivation layers. © 2003 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Electrical and optical properties of semi-insulating GaN films with the lower part of the film doped with Fe were studied. The room-temperature sheet resistivity of the films was found to be 2×10[sup 10] Ω/square. The activation energy of the dark conductivity was ∼0.5 eV which corresponds to the depth of the dominant electron traps pinning the Fermi level. The concentration of these traps was highest in the Fe-doped portion of the films and was on the order of 3×10[sup 16] cm[sup -3]. Photoinduced current transient spectroscopy also showed the presence of a high concentration of deeper electron traps with level at E[sub C]-0.9 eV and hole traps at E[sub V]+0.9 eV. These layers look very promising as insulating buffers for AlGaN/GaN transistor structures. © 2003 American Institute of Physics. [ABSTRACT FROM AUTHOR]

AlN films grown by gas-source molecular beam epitaxy were doped with different levels of Mn during growth. High resolution x-ray diffraction characterization revealed good crystallinity in single phase material, with lattice constant decreasing with increasing Mn concentration. Single phase AlMnN was found to be p type while AlMnN/AlMn mixed phase material was found to be highly conductive n type. Magnetization measurements performed with a superconducting quantum interference device magnetometer indicated ferromagnetism in single phase material persisting to 300 K and showed no evidence of room temperature magnetization in multiphase material. In particular, it was shown that Mn[sub 4]N second phases are not contributing to the magnetization in the AlMnN under optimized growth conditions. © 2003 American Institute of Physics. [ABSTRACT FROM AUTHOR]

We demonstrated that Sc[sub 2]O[sub 3] thin films deposited by plasma-assisted molecular-beam epitaxy can be used simultaneously as a gate oxide and as a surface passivation layer on AlGaN/GaN high electron mobility transistors (HEMTs). The maximum drain source current, I[sub DS], reaches a value of over 0.8 A/mm and is ∼40% higher on Sc[sub 2]O[sub 3]/AlGaN/GaN transistors relative to conventional HEMTs fabricated on the same wafer. The metal-oxide-semiconductor HEMTs (MOS-HEMTs) threshold voltage is in good agreement with the theoretical value, indicating that Sc[sub 2]O[sub 3] retains a low surface state density on the A1GaN/GaN structures and effectively eliminates the collapse in drain current seen in unpassivated devices. The MOS-HEMTs can be modulated to +6 V of gate voltage. In particular, Sc[sub 2]O[sub 3] is a very promising candidate as a gate dielectric and surface passivant because it is more stable on GaN than is MgO. [ABSTRACT FROM AUTHOR]

Lateral electron mobilities in 0.2-µm-thick n-(Ga, Mn)N films were obtained from Hall measurements, producing values of 116∼ 102 cm²/V s in the temperature range from 298 to 373 K. These values are comparable to, but slightly lower than, electron mobilities in n-GaN of the same electron concentration. By sharp contrast, analysis of the reverse saturation current in mesa Schottky diodes fabricated in the n-(Ga, Mn)N show vertical electron mobilities of 840∼336 cm²/V s in the temperature range from 298 to 373 K. This is consistent with a reduction in electron scattering by charged dislocations for vertical transport geometries [M. Misra, A. V. Sampath, and T. D. Moustakas, Appl. Phys. Lett. 76, 1045 (2000)]. [ABSTRACT FROM AUTHOR]

The Schottky barrier height of Pt contacts on n-(Ga,Mn)N (n∼3.5 × 10[sup 17] cm[sup -3]) thin films was obtained from current-voltage measurements as a function of temperature. The resulting values ranged from 0.82 ± 0.04 eV at 25°C to 0.79 ± 0.06 eV at 100°C with saturation current densities of 4.28 × 10[sup -8] A cm[sup -2] (25°C) to 8.42 × 10[sup -5] A cm[sup -2] (100°C), respectively. The barrier height at room temperature obtained from an activation energy plot was 0.91 ± 0.06 eV. The reverse current magnitude was larger than predicted by thermionic emission alone, just as in n-GaN grown in a similar fashion on Al[sub 2]O[sub 3] substrates. The measured barrier height for Pt on n-(Ga,Mn)N is lower than for the value reported on n-GaN(1.08 eV). [ABSTRACT FROM AUTHOR]

GaMnN thin films were synthesized using gas-source molecular-beam epitaxy. Mn concentrations between 3 and 12 at. % were investigated. No evidence of second-phase formation was observed by powder x-ray diffraction or high-resolution cross section transmission electron microscopy in films with 9% or less Mn. The films were n type as determined by capacitance-voltage or Hall analysis. Magnetic characterization performed using a squid magnetometer showed evidence of ferromagnetic ordering at room temperature for all samples. In agreement with theoretical predictions, material with 3% Mn showed the highest degree of ordering per Mn atom. At 320 K, the samples show a nonzero magnetization indicating a T[sub c] above room temperature. [ABSTRACT FROM AUTHOR]

We report on the growth of epitaxial CeO[sub 2] on (001) InP using hydrogen-assisted pulsed-laser deposition. Epitaxy is achieved via laser ablation of a CeO[sub 2] target in the presence of molecular hydrogen that is introduced during nucleation to reduce native In[sub 2]O[sub 3] from the InP surface. X-ray diffraction scans confirm a cube-on-cube epitaxial relationship between the oxide film and the InP substrate. Rapid heating to the deposition temperature proved important in avoiding significant decomposition of the InP surface prior to film growth. This result should enable the integration of electronic oxide functionality with InP-based semiconductor technologies, and provide a means to explore InP metal-oxide-semiconductor field-effect transistor structures. [ABSTRACT FROM AUTHOR]

Electrical and optical properties of modulation-doped p-AlGaN/GaN superlattices are compared to those of similarly doped p-GaN films. It is shown that modulation doping increases the sheet hole concentration by several times. In p-AlGaN/GaN superlattices grown on GaN underlayers, this increase is accompanied by a significant increase in hole mobility which results in a remarkable decrease in sheet resistivity of the structure compared to p-GaN films and this decrease in sheet resistivity should hold up to temperatures exceeding 350 °C. For superlattices prepared on AlGaN underlayers, the mobility decreases compared to p-GaN. In such superlattices, one also observes a strong redshift and a strong broadening of the band edge luminescence peak coming most probably from increased mosaicity and strain which would also explain the observed deterioration of mobility. The magnitude of the redshift in the position of the band edge luminescence band slightly increased upon application of reverse bias which is interpreted as a manifestation of quantum-confined Stark effect. © 2001 American Institute of Physics. [ABSTRACT FROM AUTHOR]

The sheet resistivity of oxygen-implanted n+-Al0.48In0.52As grown on InP was measured as a function of oxygen ion dose and post-implant annealing temperature. The sheet resistivity is >105 Ω/[Laplacian_variant] after implantation for doses in the range 1012–8×1013 cm-2, and increases to >107 Ω/[Laplacian_variant] after annealing at 500 °C. Temperature-dependent Hall measurements show that the resistivity of this compensated AlInAs has a thermal activation energy of 0.68 eV. Above 600 °C the damage-related compensation is removed and the material is returned to its original resistivity. We find no thermally stable, oxygen-related deep acceptors in AlInAs, in contrast to the results for AlGaAs. [ABSTRACT FROM AUTHOR]

Presents a correction on the article 'Tantalum nitride films as resistors on chemical vapor deposited diamond substrates,' which was published in the 1993 issue of the 'Journal of Applied Physics.'

GaCrN thin films were synthesized using gas-source molecular beam epitaxy. No evidence of second-phase formation was observed by powder x-ray diffraction. Magnetic characterization performed using a superconducting quantum interference device magnetometer showed evidence of ferromagnetic ordering at room temperature for all samples. In agreement with theoretical predictions, material with 3% Cr showed the highest degree of ordering. No evidence of segregation was found from secondary ion mass spectroscopy analysis. The oxygen content of the film was found to be ∼1019 cm-3. After rapid thermal annealing at temperatures up to 700 °C in a nitrogen ambient for 1 min, the room temperature saturation magnetization of the GaCrN films remained virtually unchanged, in contrast to similarly prepared GaMnN films. [ABSTRACT FROM AUTHOR]

The transport and optical properties of phosphorus-doped (Zn,Mg)O thin films grown via pulsed laser deposition (PLD) are studied. The carrier type of as-deposited (Zn,Mg)O:P films converts from n-type to p-type with increasing oxygen partial pressure. All the films exhibit good crystallinity with c-axis orientation. This result indicates the importance of oxidation conditions in realizing p-type (Zn,Mg)O:P films. The as-deposited ZnO:P film properties show a strong dependence on the deposition ambient at different growth temperatures. The resistivity of the samples deposited in O3/O2 mixture is two orders of magnitude higher than the films grown in oxygen and O2/Ar/H2 mixture. The room-temperature photoluminescence (PL) of the as-deposited films has been shown that growing in the O2/Ar/H2 mixture ambient significantly increases the band edge emission while inhibiting the visible emission. The enhanced ultraviolet (UV) emission in the films grown in O2/Ar/H2 mixture may result from hydrogen passivation of the deep level emission centers. The annealed ZnO:P films are n-type with nonlinear dependence of resistivity on annealing temperature. The resistivity increases in the films with annealing at 800°C while decreasing with further increasing annealing temperature. Strong visible light emission is observed from the ZnO:P films annealed in oxygen. [ABSTRACT FROM AUTHOR]

The damage buildup in wurtzite GaN films under light ([sup 12]C) and heavy ([sup 197]Au) ion bombardment at temperatures from -196 to 550 °C is studied by Rutherford backscattering/channeling spectrometry. A strong surface peak of lattice disorder in addition to the expected damage peak in the region of the maximum of nuclear energy loss has been observed for all implant conditions of this study. Capping of GaN with SiO[sub x] and Si[sub x]N[sub y] layers prior to implantation somewhat reduces but does not eliminate surface disordering. This suggests that nitrogen loss is not the main reason for the observed enhanced surface disorder, but, rather, the GaN surface acts as a strong sink for migrating point defects. However, pronounced loss of N during ion bombardment is observed for high dose implantation when the near-surface region is amorphized. Moreover, after amorphization, annealing at temperatures above about 400 °C leads to complete decomposition of the near-surface layer. © 2000 American Institute of Physics. [ABSTRACT FROM AUTHOR]