Improvement of Channel Mobility of GaN‐MOSFETs With Thermal Treatment for Recess Surface

Abstract

In this work, a thermal treatment technique under NH3 ambient for the recess surface of GaN‐MOSFETs is developed. Immediately following the fabrication process of the recess, the bottoms of these structures have rough surfaces and step‐terrace structures cannot be observed because of the plasma‐induced damage. However, clear step‐terrace structures are formed by the thermal treatment, and the RMS values of the surface roughness decrease from 0.26 to 0.14 nm, which is comparable to those of the as‐grown epitaxial film. In addition, it is confirmed that concentrations of impurity atoms introduced during the recess fabrication process are decreased by the thermal treatment. The channel mobility of the GaN‐MOSFETs without the thermal treatment is 118 cm2 Vs−1, whereas that of the device whose fabrication process includes the thermal treatment increased to 149 cm2 Vs−1. These results indicate that the thermal treatment under NH3 ambient is effective for reducing on‐state resistance of GaN‐MOSFETs.

Characterization technique for detection of atom-size crystalline defects and strains using two-dimensional fast-Fourier-transform sampling Moiré method

“…Since the recessed surface of the AlGaN=GaN films became rough owing to damage caused by ICP-RIE, one recessed sample was annealed in NH 3 ambient to smoothen the rough surface after RIE. 32) All samples for TEM observation were prepared using a focused ion beam (FIB). Subsequently, TEM images with high resolution (e.g., 4000 pixels × 6000 pixels) were obtained using H-9000UHR I (Hitachi).…”

Suppression of short-channel effects in normally-off GaN MOSFETs with deep recessed-gate structures

“…[35][36][37][38][39] In such cases, however, those adverse effects could be eliminated by thermal treatment. 33) Therefore, R sheet degradation in the recessedgate region could not be measured in deep recessed-gate structures.…”

“…Thermal treatment of the etched GaN surface under NH 3 at 740 °C was carried out to remove ICP-RIE damage. 33) After thermal treatment, the root mean square values of surface roughness at the bottoms of the recess structures was less than 0.15 nm. As a gate dielectric, a 30 nm thick silicon dioxide (SiO 2 ) layer was deposited on the GaN layer by the atomic layer deposition method.…”

Fabrication of Low On‐Resistance and Normally Off AlGaN/GaN Metal Oxide Semiconductor Heterojunction Field‐Effect Transistors with AlGaN Back Barrier by the Selective Area Regrowth Technique

“…Recessed-gate GaN-metal oxide semiconductor field effect transistors (MOSFETs) have recently been investigated with a view to improving device performance. [5][6][7][8][9][10][11][12] In the fabrication process of recessed-gate MOSFETs, reactive ion etching (RIE) is performed to remove the AlGaN barrier layer in the recessed structure. However, the etched surface causes degradation of performance and reliability of the MOS devices.…”

“…However, the etched surface causes degradation of performance and reliability of the MOS devices. [9,10,13] Another approach to achieve normally off devices is a selective area regrowth (SAG) technique to enable the formation of the recessed-gate structure without dry etching. [14][15][16][17] Our group recently reported the fabrication of recessed-gate MOSFET without degradation of a gate stack by SAG.…”