Analytical model of non-uniform charge distribution within the gated region of GaN HEMTs

A physics-based analytical expression that predicts the charge,electrical field and potential distributions along the gated region of the GaN HEMT channel has been developed.Unlike the gradual channel approximation(GCA),the proposed model considers the non-uniform variation of the concentration under the gated region as a function of terminal applied volt-ages.In addition,the model can capture the influence of mobility and channel temperature on the charge distribution trend.The comparison with the hydrodynamic(HD)numerical simulation showed a high agreement of the proposed model with numerical data for different bias conditions considering the self-heating and quantization of the electron concentration.The ana-lytical nature of the model allows us to reduce the computational and time cost of the simulation.Also,it can be used as a core expression to develop a complete physics-based transistorⅣmodel without GCA limitation.

Negative transconductance effect in p-GaN gate AlGaN/GaN HEMTs by traps in unintentionally doped GaN buffer layer

We investigate the negative transconductance effect in p-GaN gate AlGaN/GaN high-electron-mobility transistor(HEMT) associated with traps in the unintentionally doped GaN buffer layer. We find that a negative transconductance effect occurs with increasing the trap concentration and capture cross section when calculating transfer characteristics.The electron tunneling through AlGaN barrier and the reduced electric field discrepancy between drain side and gate side induced by traps are reasonably explained by analyzing the band diagrams, output characteristics, and the electric field strength of the channel of the devices under different trap concentrations and capture cross sections.

IMPROVED MODELING METHOD TO ACCOUNT FOR THE KINK EFFECT OF GAAS PHEMTS

Short gate-length High Electron Mobility Transistors (HEMTs) have been observed to exhibit kinks in their drain current-voltage (I-V) characteristics. To model this nonlinear effect, we present an effective approach that is easily incorporated into most existing empirical HEMT I-V models. This has been done by modifying the channel length modulation parameter to account for the kink effect. Moreover, the definitions of the left parameters in the original model will not be influenced, and the improved HEMT I-V model enhances its bias range of operation for which accuracy is maintained. The proposed modeling method is validated through DC/ Pulsed I-V as well as large-signal power measurements.

Analysis on degradation mechanisms of normally-off p-GaN gate AlGaN/GaN high-electron mobility transistor

The degradation mechanisms of enhancement-mode p-GaN gate AlGaN/GaN high-electron mobility transistor was analyzed extensively,by means of drain voltage stress and gate bias stress.The results indicate that:(ⅰ) High constant drain voltage stress has only a negligible impact on the device electrical parameters,with a slightly first increase and then decrease in output current;(ⅱ) A negative shift of threshold voltage and increased output current were observed in the device subjected to forward gate bias stress,which is mainly ascribed to the hole-trapping induced by high electric field across the p-GaN/AlGaN interface;(ⅲ) The analyzed device showed an excellent behavior at reverse gate bias stress,with almost unaltered threshold voltage,output current,and gate leakage current,exhibiting a large gate swing in the negative direction.The results are meaningful and valuable in directing the process optimization towards a high voltage and high reliable enhanced AlGaN/GaN high-electron mobility transistor.

Effects of notch structures on DC and RF performances of AlGaN/GaN high electron mobility transistors

The effects of various notch structures on direct current(DC) and radio frequency(RF) performances of AlGaN/GaN high electron mobility transistors(HEMTs) are analyzed.The AlGaN/GaN HEMTs,each with a 0.8-μm gate length,50-μm gate width,and 3-μm source-drain distance in various notch structures at the AlGaN/GaN barrier layer,are manufactured to achieve the desired DC and RF characteristics.The maximum drain current(I_(ds,max)),pinch-off voltage(V_(th)),maximum transconductance(gm),gate voltage swing(GVS),subthreshold current,gate leakage current,pulsed I-V characteristics,breakdown voltage,cut-off frequency(f_(T)),and maximum oscillation frequency(f_(max)) are investigated.The results show that the double-notch structure HEMT has a 30% improvement of gate voltage swing,a 42.2% improvement of breakdown voltage,and a 9% improvement of cut-off frequency compared with the conventional HEMT.The notch structure also has a good suppression of the current collapse.