High-Power Characteristics of GaN/InGaN Double Heterojunction Bipolar Transistors with a Regrown p-InGaN Base Layer
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High-Power Characteristics of GaN/InGaN Double Heterojunction Bipolar Transistors with a Regrown p-InGaN Base Layer Toshiki Makimoto, Yoshiharu Yamauchi, and Kazuhide Kumakura NTT Basic Research Laboratories, NTT Corporation 3-1 Morinosato Wakamiya, Atsugi-shi, Kanagawa 243-0198, Japan ABSTRACT We have investigated high-power characteristics of GaN/InGaN double heterojunction bipolar transistors on SiC substrates grown by metalorganic vapor phase epitaxy. The p-InGaN extrinsic base layers were regrown to improve ohmic characteristics of the base. Base-collector diodes showed low leakage current at their reverse bias voltages due to a wide bandgap of a GaN collector, resulting in a high-voltage transistor operation. A 90 µm x 50 µm device operated up to a collector-emitter voltage of 28 V and a collector current of 0.37 A in its common-emitter current-voltage characteristics at room temperature, which corresponds to a DC power of 10.4 W. A collector current density and a power density are as high as 8.2 kA/cm2 and 230 kW/cm2, respectively. These results show that nitride HBTs are promising for high-power electronic devices.
INTRODUCTION Nitride heterojunction bipolar transistors (HBTs) are preferable to high-power microwave electronic devices and high-power switching devices, since a high breakdown voltage is expected due to nitride semiconductors and bipolar transistors exhibit a high current density. Recently, we have reported AlGaN/InGaN/GaN HBTs with a high breakdown voltage of over 120 V. The corresponding electric field is as high as 2.3 MV/cm [1,2], which is comparable with the value calculated from the GaN bandgap [3] and much higher than the fields reported for HBTs composed of other materials, such as Si/SiGe, InGaP/GaAs, and InP/InGaAs. One of the issue to be solved for nitride HBTs was degraded ohmic characteristics of the base layer due to the etching damage [4]. We solved this issue using the regrowth technique of the p-InGaN base layer and the almost perfect ohmic characteristics were obtained. Its specific contact resistance is 7.8 x 10-4 Ωcm2 even after the dry etching and this value for a non-alloyed ohmic contact is much better than that for as-grown p-GaN (1.7 x 10-3 Ωcm2) [5]. Using this base regrowth technique, we have successfully fabricated GaN/InGaN double heterojunction bipolar transistors
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Figure 1. Schematic illustration of a GaN/InGaN DHBT on a SiC substrate grown by MOVPE. A p-InGaN extrinsic base layer was regrown to improve the ohmic characteristics of the base layer. (DHBTs) with a current gain of 3000, which is 100 times as high as our previous record [6-8]. In this work, we investigated high-power characteristics of these GaN/InGaN DHBTs on SiC substrates grown by metalorganic vapor phase epitaxy (MOVPE).
EXPERIMENTAL PROCEDURE GaN/InGaN DHBT structures were grown by low-pressure MOVPE. Figure 1 shows a schematic illustration of a GaN/InGaN HBT. The defects, which degraded ohmic characteristics of the base layer, were produced on the intrinsic p-InGaN base during
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