Electric Field Reduction in C-Doped AlGaN/GaN on Si High Electron Mobility Transistors

Abstract

I. INTRODUCTIONEMTS based on the GaN/AlGaN materials system are rapidly becoming the semiconductor device of choice for RF and power switching applications. These devices require a semi-insulating buffer to suppress leakage and punch-through. RF devices frequently make use of iron (Fe) doping to render the GaN insulating, but for the higher voltages required for many power switching applications, it has been found that carbon (C) doping delivers higher breakdown voltage and lower off-state leakage [1,2]. Unfortunately it has also been found that using carbon can result in a transitory increase in R ON , also known as current-collapse (CC), when switched from the off to the on-state [2,3]. With field plates now universally used to control surface effects, it is clear that the remaining CC in these devices mostly results from charge storage in deep levels in the buffer. Our previous studies have shown that the difference in CC between Fe and C doping results from their acceptor trap levels pinning the bulk Fermi level in the upper and lower halves of the bandgap respectively [4]. GaN:C is p-type with its low hole density, and hence high resistivity, giving long time constants for charging processes (a hole density of only 10 4 cm -3 was inferred in [5]

(Invited) Intrinsic Reliability Assessment of 650V Rated AlGaN/GaN Based Power Devices: An Industry Perspective

“…The traps are identified using current DLTS as C-atoms on an N-site at E v +0.85eV (8,9). Above V TFL , the vertical field becomes large enough to stimulate field-enhanced Poole-Frenkel current conduction (9,11) which allows the charge in the C N acceptors to leak away. As a result, the GaN buffer becomes resistive instead of capacitive.…”

Impact of buffer charge on the reliability of carbon doped AlGaN/GaN-on-Si HEMTs

“…They were biased in the off-state with V GS = −7V and V DS = 100V for a time period of 1000s before pulsing to the on-state with V GS = 0V, V DS = 1V. This corresponds to a "worst case" V DS for dynamic R ON measurement [23,24]. The on-state current, I DON , was then recorded for 1000s allowing the device to return towards equilibrium.…”

Control of Buffer-Induced Current Collapse in AlGaN/GaN HEMTs Using SiNx Deposition

“…VD =100V has been chosen for the OFFstate stress as this is close to the peak dynamic Ron seen on these types of devices. [13] Wafer A exhibits significant current collapse and wafer C and D have almost none. Wafer B corresponds to close to optimum with a low off-state drain leakage (shown in [10]) and low current-collapse.…”

“…The lateral distribution of charges in the C:GaN layer will impact not only current collapse in a device but also the electric field distribution in the channel [12,13]. Fig.…”