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This article reports on the experimental and analytical determination of the optimum carbon concentration in GaN to achieve enhanced breakdown in AlGaN/GaN high-electron mobility transistors (HEMTs). The lateral breakdown voltage increases when carbon doping is increased from 3 × 1018 to 1019 cm−3 beyond which it decreases, whereas there is no substantial enhancement in the vertical breakdown voltage with carbon doping. We invoke carrier statistics in a compensated semiconductor vis-à-vis the formation energy of carbon-occupying Ga (or N) vacancies to explain the observed buffer leakage. Temperature-dependent data indicate that the buffer leakage current is due to hopping transport, the activation energy of which yields the positions of the defect states within the bandgap. The increase in buffer leakage beyond optimum C concentration is attributed to the formation of shallow donor traps by carbon atoms occupying Ga vacancies (CGa). The observations correlated with the relative intensities of the defect-mediated peaks in the cathodoluminescence (CL) data of the samples. Based on our findings, a C doping beyond 1019 cm−3 is not recommended for GaN buffers in order to achieve high breakdown voltages. [ABSTRACT FROM AUTHOR]

We report on the quantitative estimates of various metrics of performance for $\beta $ -Ga2O3-based high electron mobility transistors (HEMTs) for RF and power applications and compare them with III-nitride devices. Device parameters such as electron velocity and current density are estimated based on an optical phonon model reported earlier. 2-D simulation using an appropriate velocity-field relationship was employed to study the device characteristics and to assess the RF performance. It is found that despite a lower cutoff frequency, $\beta $ -Ga2O0 HEMTs are likely to provide higher RF output power compared to GaN HEMTs in the low-frequency regime. However, the thermal resistance (TR) and the channel temperature of $\beta $ -Ga2O3 HEMTs are expected to be significantly higher than those of GaN HEMTs which will pose serious limitations on heat dissipation. $\beta $ -Ga2O3 modulation doped field effect transistor on extremely thinned substrates will have similar TR s as compared to GaN devices on GaN substrates. The cutoff frequency was found to drop by 50% as the power dissipation increases from 1 to 7 W/mm. On the other hand, for estimates of dc power switching performance, we estimate the net losses as a function of device periphery and find that $\sim {8}\times $ – ${10}\times $ lower electron mobility in Ga2O3 devices compared to that in AlGaN/GaN HEMTs will limit its dc switching as well as its ON- state performance in terms of efficiency, loss, and current carrying capability although the blocking voltage can be much higher than in GaN. [ABSTRACT FROM AUTHOR]

We report on the demonstration and investigation of Ta2O5 as high-k dielectric for InAlN/GaN-MOS high-electron mobility transistor (HEMT)-on-Si. Ta2O5 of thickness 24 nm and dielectric constant ~30 was sputter deposited on InAlN/GaN HEMT and was investigated for different post deposition anneal (PDA) conditions. The gate leakage was 16 nA/mm at −15 V which was ~five orders of magnitude lower compared to reference HEMT. The 2-D electron gas (2-DEG) density was found to vary with annealing temperature suggesting the presence of net charge at the Ta2O5/InAlN interface. Dispersion in the capacitance–voltage (${C}$ – ${V}$) characteristics was used to estimate the frequency-dependent interface charge, while energy band diagrams under flat band conditions were investigated to estimate fixed charge. The optimum anneal condition was found to be 500 °C which has resulted into a flat band voltage spread ($\Delta {V}_{\text {FB}}$) of 0.4 V and interface fix charge (${Q} _{\text {f}}$) of ${3.98} \times {10}^{{13}}$ cm $^{-2}$. X-ray photoelectron spectroscopy spectra of as-deposited and annealed Ta2O5film were analyzed for Ta and O compositions in the film. The sample annealed at 500 °C has shown Ta:O ratio of 0.41. X-ray diffraction analysis was done to check the crystallization of amorphous Ta2O5 film at higher annealing temperatures. [ABSTRACT FROM AUTHOR]

We investigate the vertical leakage mechanism in metal–organic chemical vapor deposition-grown carbon (C)-doped AlGaN/GaN High Electron Mobility Transistors (HEMTs) on 6-in silicon wafer. Substrate bias polarity-dependent ${I}$ – ${V}_{s}$ , temperature-dependent fitting, and band diagram analysis pointed to the Poole–Frenkel (P–F) type of conduction mechanism for vertical transport in the devices with breakdown as high as 580 V for a buffer of $\textsf {4}~\mu \text{m}$. Trap activation energy of 0.61 eV was estimated from the P–F fitting which matches well with values reported in the literature. We propose that higher dislocation density leads to shallower traps in the buffer and build an analytical model of dislocation-mediated vertical leakage around this. The variation in leakage as a function of dislocation density at a given field is predicted and is found to be the most abrupt in the range from $\sim 10^{\textsf {7}}$ to $\sim 10^{\textsf {9}}$ cm $^{-\textsf {2}}$ of dislocation density. This can be attributed to a sharp decrease in trap activation energy in the above range of dislocation density, possibly due to complex formation between point defects and dislocations. [ABSTRACT FROM AUTHOR]

We report on the band offset and interfacial electronic properties of e-beam evaporated HfO2 gate dielectrics on III-nitride device stacks on Si. A conduction band offset of 1.9 eV is extracted for HfO2/GaN along with a very low density of fixed bulk and interfacial charges for optimally annealed samples. Normally-ON HfO2/AlGaN/GaN metal–insulator–semiconductor high-electron-mobility transistors exhibit negligible shifts in threshold voltage, transconductances of 120 mS/mm for 3- $\mu \text{m}$ gate length devices, and three-terminal off-state gate leakage currents of 55 nA/mm at a ${V}_{D}$ of 100 V. Dynamic capacitance dispersion measurements in the temperature range of 25 °C–200 °C show two peaks at the AlGaN/GaN interface corresponding to slow and fast interface traps with a peak ${D}_{\text {it}}$ of ${5.5}\times {10}^{13}$ and ${1.5} \times {10}^{13}$ eV−1cm−2 respectively as a function of Fermi level position above ${E}_{C}$. The HfO2/AlGaN interface exhibits a reasonably constant peak ${D}_{\text {it}}$ of ${2} \times {10}^{13}$ – ${4.4} \times {10}^{13}$ eV−1cm−2 at trap levels of 0.42–0.72 eV below ${E}_{\text {C}}$. Hysteretic pulsed $I_{D}$ – $V_{G}$ measurements revealed a negative shift in threshold voltages indicative of unoccupied donor-like trap states at the HfO2/AlGaN interface and comparable ${D}_{\text {it}}$ to that inferred from conductance measurements. [ABSTRACT FROM AUTHOR]

An explanation for the observed drain current collapse in AlGaN/GaN high electron mobility transistors is presented. The drain current–voltage (I\--V) characteristics which show this undesirable behavior have been modeled using the physics-based ATLAS device simulator by Silvaco. A basic theory for the determination of virtual gate length for a three terminal device has been developed and used in the simulation. The simulated I\--V characteristics closely match the experimental results. This paper suggests a model based on formation of a high resistance region under the virtual gate in the 2-D electron gas channel. The resistance of this region changes abruptly at a critical lateral electric field due to application of drain–source voltage. This abrupt change has been found to be a function of channel temperature. The dynamic behavior of this high resistance region has been proposed to be the cause of drain current collapse. [ABSTRACT FROM AUTHOR]