Polarization doping modulated heterojunction electron gas in AlGaN/GaN CAVETs

Abstract

A common AlGaN/GaN current-aperture vertical effect transistor (CAVET) with a SiO 2 current blocking layer on the GaN substrate is compared to two similar structures with the stepped and linearly graded AlGaN barrier layer, respectively. The approach resulted in high threshold voltages (V th ) of −2.6 V and −3.6 V, compared to V th = −4.4 V for the common device. And the breakdown voltage of two modified CAVETs was increased from 541 V to 711 V and 613 V, respectively. This reveals the great potential of polarization doping for fabricating enhancement-mode and high-voltage power transistors. A mechanism accounting for the improvement in the device performance by modulating the heterojunction electron gas (HEG) is presented. Meanwhile the stepped graded AlGaN is discovered to be better than the linearly graded AlGaN in modulating the HEG. Furthermore, a trench structure is involved in the AlGaN/GaN CAVET with the stepped graded AlGaN in order to obtain an enhancement-mode device. A positive threshold voltage of 0.6 V and a breakdown voltage exceeding 800 V are demonstrated.

Recent Advances in GaN‐Based Power HEMT Devices

“…[ 257–259 ] For the cost and process‐simplifying consideration, several quasivertical GaN power diodes and transistors on the foreign substrates were developed, which consist of the vertical drift region and lateral spreading layers. [ 260–264 ] In particular, the current aperture vertical electron transistor (CAVET) [ 265–268 ] and trench CAVET [ 269–271 ] can operate the device by controlling the 2DEG channel, similarly to the lateral GaN HEMTs. Recently, the advanced vertical and quasi‐vertical GaN Schottky barrier diodes (SBDs), [ 253,272,273 ] junction barrier Schottky diodes, [ 274 ] fin MOSFETs, [ 275 ] trench MOSFETs, [ 276 ] superjunction diodes [ 277 ] and PN diodes [ 278–280 ] have successively raised the V BD from 600 to 4000 V with low R on .…”

Vertical GaN and Vertical Ga2O3Power Transistors: Status and Challenges

“…[25] Since then, several other CAVET demonstrations have been made. [14,26,27] The CAVET device design in GaN (to an extent) is analogous to the D-MOSFET, which has been explored in Si and SiC. [15] The CAVET utilizes a lateral AlGaN/GaN 2D electron gas (2-DEG) based highly conductive channel.…”

“…The regrowth and planarization processes may result in some leakage issues in the off state as discussed in the literature. [ 14,26–28 ] However, Nie et al have reported a high performing, normally‐off 1500 V, 2.2 mΩ cm 2 device, thus, demonstrating the potential of this device design. [ 14 ] Recently, Tanaka et al have demonstrated ion implantation based 1.2 kV vertical GaN planar MOSFET with low on‐resistance of 1.4 mΩ cm 2 .…”

Study of AlGaN/GaN Vertical Superjunction HEMT for Improvement of Breakdown Voltage and Specific On-Resistance

“…Research on what methods are used to improve the conduction characteristics of vertical devices has become a hot spot in this field. The introduction of structures such as P-buried layer [13], superjunction (SJ) [14]- [17] and current barrier layer (CBL) of SiO 2 material [18] has promoted the improvement of vertical device performance and laid the foundation for the current demand for a wider range of applications. However, the existing technology to reduce the specific on-resistance (R onA ) of vertical devices is still relatively limited.…”