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[EN]We report on the modeling of self-heating in GaN-based devices. While a constant thermal resistance is able to account for the self-heating effects at low power, the decrease of the thermal conductance of semiconductors when the lattice temperature increases, makes necessary the use of temperature dependent thermal resistance models. Moreover, in order to correctly account for the steep increase of the thermal resistance of GaN devices at high temperature, where commonly used models fail, we propose a non-linear model which, included in an electro-thermal Monte Carlo simulator, is able to reproduce the strongly non-linear behavior of the thermal resistance observed in experiments at high DC power levels. The accuracy of the proposed non-linear thermal resistance model has been confirmed by means of the comparison with pulsed and DC measurements made in devices specifically fabricated on doped GaN, able to reach DC power levels above 150 W mm−1 at biases below 30 V., NRF2017-NRFANR003 GaNGUN project, the Spanish MINECO and FEDER through project TEC2017-83910-R and the Junta de Castilla y León and FEDER through project SA254P18.

AlN/GaN metal–insulator–semiconductor high electron mobility transistors (MISHEMTs) on silicon substrate using in situ SiN as gate dielectric were fabricated and their RF power performance at mobile system-on-chip (SoC) compatible voltages was measured. At a mobile SoC-compatible supply voltage of V d = 3.5 V/5 V, the 90 nm gate-length AlN/GaN MISHEMTs showed a maximum power-added efficiency of 62%/58%, a maximum output power density (P outmax) of 0.44 W mm−1/0.84 W mm−1 and a linear gain of 20 dB/19 dB at the frequency of 5 GHz. These results suggest that the in situ-SiN/AlN/GaN-on-Si MISHEMTs are promising for RF power amplifiers in 5G mobile SoC applications.

Current-voltage-temperature characteristics (0oC to 150oC) of SBDs on highly compensated 15µm and 30µm n-type GaN drift layer were measured for voltages up to -300V and up to -800V, respectively. When the temperature is between 75oC and 100oC, both SBDs exhibited a similar change in conduction mechanism from thermionic field emission (TFE) to thermionic emission (TE) due to the activation of N-vacancies (VN) (Ea=-1.67eV). However, at high voltages when the temperature is >100oC, the conduction mechanism changes from TE to TFE due to the de-trapping of electrons from the activated carbon-traps (Ea=+0.69eV) in the grown DLs.

Vertically ordered hexagonal boron nitride (h-BN) films were successfully sputtered on AlGaN/GaN heterostructure (HS) using High Power Impulse Magnetron Sputtering at room temperature. The h-BNs vertical ordering along the (0002) plane was confirmed using high-resolution transmission electron microscopy. After the h-BN deposition, degradation of two-dimensional electron gas (2DEG) properties was observed in AlGaN/GaN HS. Full recovery of 2DEG mobility, along with an improvement in sheet resistance and an increase in sheet carrier concentration was obtained after rapid thermal annealing at 500°C for 300s in a N2 atmosphere, which is due to the reduction of sputtering related structural damage.

GaN-on-Si high electron mobility transistors (HEMTs) with 80 nm gate length fabricated using Si CMOS-compatible Ta/Al ohmic and Ti/Al gate contacts are reported in this work. The device with a source-drain distance (Lsd) of 750 nm exhibited a high cut-off frequency (fT) of 210 GHz. An off-state breakdown voltage (BV) of 46 V and a high Johnson's figure-of-merit (= fT × BV) of 8.8 THzV have been achieved in a device with Lsd of 1.5 μm. These results show the great potential of GaN-on-Si HEMTs to realize high performance-to-cost ratio mm-wave devices through mass production using current Si foundries.

A deeply-scaled GaN-on-Si high electron mobility transistor (HEMT) with a record-high cut-off frequency (fT) of 310 GHz has been demonstrated. The device has an InAlN/GaN heterojunction structure, a source-drain spacing of 400 nm, and a gate length of 40 nm. The device exhibited a high drain current of 2.34 A/mm, a peak transconductance of 523 mS/mm, and a gate-to-drain breakdown voltage (BVgd) of 15 V. A Johnson's figure-of-merit (FOM = fT × BV) of 4.65 THz-V has been achieved, which is comparable to those reported in GaN-on-SiC. These results indicate GaN-on-Si transistors are promising in low-cost emerging mm-wave applications.

We show that a vacancy-controlled model can explain the experimentally observed negative dependence on the stress temperature of GaAs/AlGaAs heterojunction bipolar transistors' degradation by non-radiative defects. The driving force (osmotic force) of the degradation versus the bias stress temperature is calculated and a decreasing temperature dependence is found. This model, which has previously been applied to strained-layer lasers and light emitting diodes, will help us understand the reported experimental observations on the temperature-acceleration tests for the GaAs/AlGaAs-based heterostructure devices such as heterojunction bipolar transistors.

A detailed DC characterization of metamorphic InP/InGaAs/InP double heterojunction bipolar transistors (DHBT's) in the temperature range of 300 K to 400 K was carried out and the carrier transport properties were investigated. Our experiments reveal that band-to-band recombination is the dominant mechanism for the base current indicating the good base material quality for the metamorphic HBT structures.

The effect of silicon nitride passivation on the electrical characteristics of InP/InGaAs heterojunction bipolar transistors (HBT's) has been investigated comprehensively. The major degradations of I–V characteristics identified in our InP/InGaAs HBT's are: (1) the decrease of current gain due to a significant increase in the forward base leakage current and (2) large increase of base-collector (B-C) and base-emitter (B-E) reverse leakage currents. We found that different physical origins should be attributed to these two degradation behaviors.

The distribution of trap energy (DTE) levels was observed in the energy band gap of buffer GaN by temperature-dependent current transient measurements on AlGaN/GaN HEMTs under fully ON drain-stress (VD[ON]_Stress) conditions. The activation energies (Ea's) obtained from current transients increase with increasing VD[ON]_Stress. Using a multitrap energy (MTE) model, the applied-VD[ON]_Stress-dependent Ea is attributed to DTE levels in the GaN energy band gap, rather than to discrete single trap energy levels. An effective activation energy (Ea_eff) corresponding to trap energy levels activated by the applied VD[ON]_Stress is thus obtained. This observation is validated with two-dimensional numerical simulations. This study will help device designers develop a "DTE-dependent" emission time constant model that is readily applicable for the reliability modelling of future GaN-based circuits.

We have demonstrated 0.17-µm gate-length In0.17Al0.83N/GaN high-electron-mobility transistors (HEMTs) on Si(111) substrates using a non-gold metal stack (Ta/Si/Ti/Al/Ni/Ta) with a record-low ohmic contact resistance (Rc) of 0.36 Ω mm. This contact resistance is comparable to the conventional gold-based (Ti/Al/Ni/Au) ohmic contact resistance (Rc = 0.33 Ω mm). A non-gold ohmic contact exhibited a smooth surface morphology with a root mean square surface roughness of ~2.1 nm (scan area of 5 × 5 µm2). The HEMTs exhibited a maximum drain current density of 1110 mA/mm, a maximum extrinsic transconductance of 353 mS/mm, a unity current gain cutoff frequency of 48 GHz, and a maximum oscillation frequency of 66 GHz. These devices exhibited a very small (

This work investigates the conduction mechanism of non-gold Ta/Si/Ti/Al/Ni/Ta ohmic contact in un-doped AlGaN/GaN high-electron-mobility transistors (HEMTs) grown on Si. Temperature-dependent current–voltage (I–V) measurements reveal that the conduction occurs primarily via thermionic emission (TE). The extracted mean barrier height (ΦB) values are 0.113 and 0.121 eV and the mean contact resistance (Rc) values are 0.24 and 0.28 Ω mm, for annealing temperatures of 850 and 900 °C, respectively. The low Rc is attributed to the formation of low work function TixSiy at the metal–semiconductor interface. The high-resolution transmission electron microscopy (HR-TEM) and energy-dispersive X-ray spectroscopy (EDX) analysis provide further structural evidence in support of the TE mechanism. Accepted version

The impact of low-k dielectric benzocyclobutane (BCB) encapsulation on the electrical performance and structural stability of AlGaN/GaN HEMTs on Si were investigated. After BCB encapsulation, devices exhibited no degradation in their drain current density, extrinsic transconductance and small signal microwave performances. The curing temperature (280 °C) of BCB layer had no influence on the device electrical performances. Compared to devices without BCB encapsulation, the BCB encapsulated devices achieved ~2 orders of magnitude lower gate- and drain-leakage current. An order of magnitude lower surface leakage current was also observed by BCB encapsulation between the two adjacent mesas. Due to the reduction of leakage currents, ~2-times increase of OFF-state breakdown voltage was observed. In addition, the 9-µm-thick BCB encapsulation layer also helps to have structurally stable air bridges. This work demonstrates the low-k dielectric BCB as a viable solution for the complete encapsulation of GaN HEMTs and ICs.

AlGaN/GaN high-electron-mobility transistors (HEMTs) with a 0.15-µm gate were fabricated on a Si substrate with an 8-nm-thick AlGaN barrier. The device exhibited a unity current gain cutoff frequency fT of 63 GHz and maximum oscillation frequency fmax of 124 GHz. Its three-terminal OFF-state breakdown voltage BVgd is as high as 132 V. The estimated Johnson's figure of merit (=BVgd × fT) is 8.32 × 1012 V/s (8.32 THz·V), which is the highest value ever reported for a conventional SiN-passivated T-gate AlGaN/GaN HEMTs on a Si substrate without an additional field plate or gamma gate.

We report the molecular beam epitaxial (MBE) growth of epitaxial InP using a valved phosphorous cracker cell at a range of cracking zone temperature (T cr=875°C to 950°C), V/III flux ratio (V/III=1.2 to 9.3) and substrate temperature (T s=360°C to 500°C). From Hall measurements, the as-grown epitaxial InP on InP (100) substrate was found to be n-type. The background electron concentration and mobility exhibited a pronounced dependence on the cracking zone temperature, V/III flux ratio and substrate temperature. Using a cracking zone temperature of 850°C, the highest 77 K electron mobility of 40900 cm2/Vs was achieved at a V/III ratio of 2.3 at a substrate temperature (T s) of 440°C. The corresponding background electron concentration was 1.74×1015 cm-3. The photoluminescence (PL) spectra showed two prominent peaks at 1.384 eV and 1.415 eV, with the intensity of the low-energy peak becoming stronger at higher cracking zone temperatures. The surface morphology deteriorated following a reduction in the V/III ratio or an increase in the substrate temperature. In the extreme case, formation of free indium droplets and severe surface faceting occurred.