The physical mechanism of dispersion caused by AlGaN/GaN buffers on Si and optimization for low dispersion

Abstract

In this paper a measurement methodology, using a two-dimensional electron gas (2DEG) resistor, is used to evaluate the dispersion of three different type of buffers, namely a step graded buffer, a buffer with low temperature (LT) AlN interlayers and a superlattice buffer. Together with a dedicated Design of Experiments (DOE), these measurements allowed us to identify the physical origin of the dispersion and identify the key parts of the buffer which influence the buffer-induced dispersion of the 2DEG.

Probing the effect of point defects on the leakage blocking capability of Al0.1Ga0.9N/Si structures using a monoenergetic positron beam

“…Because point defects in GaN and AlGaN also act as electron/hole trap centers, the study of their charge/discharge processes is of high importance in understanding the buffer related dispersion and current collapse issues in power transistors. 15 Despite tremendous research efforts, C-doping related point defect generation, buffer leakage mechanism, and buffer dispersion have by far not been well understood. Positron annihilation is a powerful technique to evaluate vacancy-type defects in semiconductors, 16,17 and defects in group-III nitrides have been successfully investigated using this method.…”

Lateral Charge Transport in the Carbon-Doped Buffer in AlGaN/GaN-on-Si HEMTs

“…Fig. 1(c) shows the lumped-element representation of the device structure including the primary vertical leakage paths and capacitances normally used to interpret substrate bias experiments assuming 1D conduction [11,[13][14][15][16][17][18][19]. Only negative substrate bias, VSUB, is considered here since this corresponds to the polarity experienced under the drain in a transistor under OFF state conditions.…”

“…When employing standard approaches to improve the lateral breakdown strength, such as intentional incorporation of carbon (C) dopants, dynamic on-resistance (a time dependent on-resistance resulting from charge storage in either surface or bulk traps that can affect the performance of the device during switching) degrades significantly [5]- [8] impacting the power device efficiency. Surface trapping can be very effectively controlled by the use of field plates [9], but bulk trapping is inherent in all single-heterojunction HEMTs due to the necessity to include deep-level dopants in the GaN buffer to control bulk leakage and short-channel effects [10,11]. Carbon has a complex range of deep levels in the gap, but the most important is an acceptor sitting 0.9 eV above the valence band [12].…”

Optimization of the source field‐plate design for low dynamic RDS‐ON dispersion of AlGaN/GaN MIS‐HEMTs

“…The increase of the dynamic R DS‐ON , also called current collapse or R DS‐ON dispersion, is the main concern for the GaN HEMT, becoming an important topic in the scientific literature . Trapping states in GaN HEMTs responsible for the dynamic R DS‐ON increase have been located at the surface , under the gate dielectric and in the barrier , in the back barrier and buffer layers .…”

“…Thus, the first step for a low dynamic R DS‐ON is to improve the device fabrication, starting from the epitaxial growth of the buffer up to the surface passivation of the device . The second step is to use gate and source field‐plates to redistribute the peak of the electric field .…”