Deep-Donor-Induced Suppression of Current Collapse in an AlGaN-GaN Heterojunction Structure Grown on Si

Abstract

TCAD simulation was performed to investigate the material properties of an AlGaN/GaN structure in Deep Acceptor (DA)-rich and Deep Donor (DD)-rich GaN cases. DD-rich semi-insulating GaN generated a positively charged area thereof to prevent the electron concentration in 2DEG from decreasing, while a DA-rich counterpart caused electron depletion, which was the origin of the current collapse in AlGaN/GaN HFETs. These simulation results were well verified experimentally using three nitride samples including buffer-GaN layers with carbon concentration ([C]) of 5 × 10 17 , 5 × 10 18 , and 4 × 10 19 cm −3. DD-rich behaviors were observed for the sample with [C] = 4 × 10 19 cm −3 , and DD energy level E DD = 0.6 eV was estimated by the Arrhenius plot of temperature-dependent I DS. This E DD value coincided with the previously estimated E DD. The backgate experiments revealed that these DD-rich semi-insulating GaN suppressed both current collapse and buffer leakage, thus providing characteristics desirable for practical usage.

Zn-Doped GaN Comprising the Gate Structure of Normally Off AlGaN/GaN-HFETs

“…3(c), to estimate ET. The device structure and process used here are the same as those previously reported in [1] and [11]. Here, [Zn] is 1 × 10 19 cm -3 in size in the 900-nm GaN:Zn layer.…”

“…Therefore, we must estimate the ET -EV value. To this end, the team used the same method as reported by Tanaka et al [11]; Fig. 3(c) includes the electrical bias configuration for this measurement.…”

“…3(c) includes the electrical bias configuration for this measurement. As discussed in [11], a negative gate-source voltage (Vgs) negatively charges Zn, assuming Zn as a deep acceptor (DA) in GaN, and consequently, the electrons in the 2DEG exponentially dissipate during the ET dependent decay time of τ to decrease id. The temperature dependence of the current transient measurements for GaN:Zn is shown in Fig.…”

“…For this purpose, we prepared back-gate structured transistors including the GaN:Zn layer; these devices have the source and drain electrodes on their surface, as well as on the gate formed on the back side of the substrate used. After the gate is negatively biased to the source, the charged state of Zn changes; thus, the drain current (id) of the transistor decays in a timedependent manner, reflecting the energy level of Zn within the GaN band structure [11]. Section IV describes the main body, including the transistor characteristics of AlGaN/GaN HFETs with a top-mesa structure made of GaN:Zn.…”