Buffer Design to Minimize Current Collapse in GaN/AlGaN HFETs

Abstract

The bulk trap induced component of current collapse in GaN/AlGaN HFETs is studied in drift diffusion simulations, distinguishing between acceptor traps situated in the top and bottom half of the bandgap, with Fe and C used as specific examples. It is shown that Fe doping results in an inherent but relatively minor contribution to dispersion under pulse conditions. This simulation is in reasonable quantitative agreement with double pulse experiments. Simulations using deep-level intrinsic growth defects produced a similar result. By contrast, carbon can induce a strong current collapse which is dependent on doping density. The difference is attributed to whether the trap levels, whether intrinsic or extrinsic dopants, result in a resistive n-type buffer or a p-type floating buffer with bias dependent depletion regions. This insight provides a key design concept for compensation schemes needed to ensure semiinsulating buffer doping for either RF or power applications.

Modelling and Simulation of Normally-Off AlGaN/GaN MOS-HEMTs

“…To ensure high resistivity of GaN:C layer a deep acceptor trap level located at 0.9eV [7] above the valence band and traps density 1 × 10 18 cm −3 was introduced. A shallow donor traps concentration 1×10 15 cm −3 [8] was assumed for all nitrides layers. The recess depth in Al 0.25 Ga 0.75 N barrier layer under gate electrode and thickness of gate dielectric was 20 and 50nm, respectively.…”

Impact of residual carbon on two-dimensional electron gas properties in AlxGa1−xN/GaN heterostructure

“…4 The electrical property of GaN buffer layer (GaN BL) in the HEMT structure is one of the critical parameters that will influence the final device reliability. [4][5][6] Firstly, the GaN BL has to be semi-insulating (SI) to prevent unwanted current paths underneath the two-dimensional electron gas (2DEG) channel and also to obtain high breakdown voltage with low leakage current. One effective way to achieve this is to introduce acceptor-like impurities, like iron 7 or carbon, [8][9][10] during growth of the GaN BL; however, iron doping has a memory effect rendering doping profile difficult to control.…”

“…Secondly, in order to alleviate the trapping effect that causes failure of device characteristics, known as current collapse, the level of acceptor-like impurities in the vicinity of 2DEG channel should be minimized. 5,6,11 Apparently, these two requirements for the GaN BL are in conflict with each other. Therefore, the level of acceptor-like impurities in the GaN BL needs to be carefully defined and optimized.…”

Self-heating and polarization effects in AlGaN/AlN/GaN/AlGaN based devices

“…In the GaN buffer, we use carbon acceptor traps at an energy of ET=EV+0.9 eV with a density of 1×10 17 cm -3 which act to reduce a leakage current in the buffer. Additionally, we have used traps corresponding to iron with a concentration of 4×10 18 cm -3 at ET=EV+0.6 eV in the Al0.1Ga0.9N back barrier [9]. The GaN cap donor concentration was set to be 5×10 20 cm -3 , which is similar to that reported in [10] with energy level of ET=EC-0.5 eV [9].…”