Effect of Mg ionization efficiency on performance of Npn AlGaN/GaN heterojunction bipolar transistors

Abstract

A drift-diffusion transport model has been used to examine the performance capabilities of AIGaN/GaN Npn heterojunction bipolar transistors (HBTs). The Gumrnel plot from the first GaN-based HBT structure recently demonstrated is adjusted with simulation by using experimental mobility and lifetime reported in the literature. Numerical results have been explored to study the effect of the p-type Mg doping and its incomplete ionization in the base.The high base resistance induced by the deep acceptor level is found to be the cause of limiting current gain values. Increasing the operating temperature of the device activates more carriers in the base. An improvement of the simulated current gain by a factor of 2 to 4 between 25 and 300"C agrees well with the reported experimental results. A preliminary analysis of high frequency characteristics indicates substantial progress of predicted rf performances by operating the device at higher temperature due to a reduced extrinsic base resistivity.

Temperature dependent I-V characteristics of AlGaN/GaN HBTs and GaN BJTs

“…In the Ic range of 10-4_10-3 A, /3 increases with increasing temperature. This is consistent with the simulation result [1], which was attributed to the spreading of 2 dimensional base current at higher temperature owing to the higher degree of Mg activation. At higher currents (-10-3 A) where the base-emitter recombination current is negligible, the device gain shows little change with temperature, as expected for HBTs.…”

“…Some groups have reported an increased current gain I of AlGaN/GaN heterojunction bipolar transistors (HBTs) at higher temperatures due to enhanced ionization of deep Mg accepters in the base [1], while others have reported an increase in J at lower temperatures [2]. In this paper, we show that this discrepancy can be largely attributed to the different operating current levels of the devices.…”

Optimization of conductivity in p-type GaN∕InGaN-graded superlattices

“…The GaN barrier is assumed to be doped at ϳ6.4ϫ 10 18 cm −3 , which corresponds to an areal acceptor doping density of 9.64ϫ 10 12 cm −2 per period. [23][24][25] To reduce the barrier height, a new structure was designed ͑graded SL-A͒ by inserting a linearly graded In x Ga 1−x N layer in the p-type SLs between the GaN barrier and InGaN QW. The schematic charge distribution and VB structure are shown in Figs.…”

Equivalent-Circuit Analysis for the Electroluminescence-Efficiency Problem of InGaN/GaN Light-Emitting Diodes

“…22 was carried out under DCbias conditions, a temperature compensation may be added to the above estimation as hole generation depends on temperature. 23) Temperature of Mg-doped layers is approximated to be proportional to current and to reach 400 K at 1 A. The acceptor ionization energy was tentatively taken to be 0.12 eV to obtain the change in hole concentration, which is denoted by in Fig.…”