Toshiya Tabuchi

Uniform Growth of AlGaN/GaN High Electron Mobility Transistors on 200 mm Silicon (111) Substrate

Crack-free AlGaN/GaN high-electron-mobility transistors (HEMTs) grown on a 200 mm Si substrate by metal–organic chemical vapor deposition (MOCVD) is presented. As grown epitaxial layers show good surface uniformity throughout the wafer. The AlGaN/GaN HEMT with the gate length of 1.5 µm exhibits a high drain current density of 856 mA/mm and a transconductance of 153 mS/mm. The 3.8-µm-thick device demonstrates a high breakdown voltage of 1.1 kV and a low specific on-resistance of 2.3 mΩ cm2 for the gate–drain spacing of 20 µm. The figure of merit of our device is calculated as 5.3×108 V2 Ω-1 cm-2.

Normally-OFF Al2O3/AlGaN/GaN MOS-HEMT on 8 in. Si with Low Leakage Current and High Breakdown Voltage (825 V)

We report recessed-gate Al2O3/AlGaN/GaN normally-OFF metal–oxide–semiconductor high-electron-mobility transistors (MOS-HEMTs) on 8 in. Si. The MOS-HEMTs showed a maximum drain current of 300 mA/mm with a high threshold voltage of +2.4 V. The quite low subthreshold leakage current (~10−8 mA/mm) yielded an excellent ON/OFF current ratio (9 × 108) with a small, stable subthreshold slope of 74 mV/dec. An atomic-layer-deposited Al2O3 layer effectively passivates, as no significant drain current dispersions were observed. A high OFF-state breakdown voltage of 825 V was achieved for a device with a gate-to-drain distance of 20 µm at a gate bias of 0 V.

Growth of silicon-doped Al0.6Ga0.4N with low carbon concentration at high growth rate using high-flow-rate metal organic vapor phase epitaxy reactor

The relationship between the carbon concentration and electrical characteristics of silicon-doped AlGaN (Al > 0.5) was investigated using a high-flow-rate metal organic vapor phase epitaxy (MOVPE) reactor. The carbon concentration and electrical properties of AlGaN (Al > 0.5) were measured as a function of the growth rate, V/III ratio, and growth temperature. The growth rate of Al0.6Ga0.4N was linearly controlled up to 7.2 µm/h under a constant ammonia (NH3) flow rate. However, a decrease in V/III ratio resulted in an increase in carbon concentration to 8 × 1017 cm−3. With increased growth temperature, the carbon concentration decreased to less than 2 × 1017 cm−3 without showing any reduction in growth rate. As a result, n-type Al0.6Ga0.4N with a carrier concentration of 5.4 × 1018 cm−3 and a resistivity of 2.2 × 10−2 Ωcm was obtained.

Opportunities and challenges in GaN metal organic chemical vapor deposition for electron devices

The current situation and next challenge in GaN metal organic chemical vapor deposition (MOCVD) for electron devices of both GaN on Si and GaN on GaN are presented. We have examined the possibility of increasing the growth rate of GaN on 200-mm-diameter Si by using a multiwafer production MOCVD machine, in which the vapor phase parasitic reaction is well controlled. The impact of a high-growth-rate strained-layer-superlattice (SLS) buffer layer is presented in terms of material properties. An SLS growth rate of as high as 3.46 µm/h, which was 73% higher than the current optimum, was demonstrated. As a result, comparable material properties were obtained. Next, a typical result of GaN doped with Si of 1 × 1016 cm−3 grown at the growth rate of 3.7 µm/h is shown. For high-voltage application, we need a thick high-purity GaN drift layer with a low carbon concentration, of less than 1016 cm−3. It is shown that achieving a high growth rate by precise control of the vapor phase reaction is still challenge in GaN MOCVD.

Study on AlGaN/GaN growth on carbonized Si substrate

AlGaN/GaN films were grown on carbonized Si(111) substrates, which were employed to prevent impurities such as residual Ga atoms from reacting and deteriorating the surface of Si substrates. The cleaning process for the flow channel in metal organic chemical vapor deposition (MOCVD) could effectively be eliminated by using this carbonized Si substrate, and high-quality AlGaN/GaN films were obtained.

High growth rate of AlGaN for buffer structures for GaN on Si to increase throughput

Throughput requirement of the epitaxial process of GaN on Si is described. The impact of the growth rate of AlGaN for the buffer layer of GaN on Si is highlighted. In the attempt of growing GaN on Si, we have tested a production scale high flow speed MOVPE reactor (TAIYO NIPPON SANSO UR25k) for 6 inch X 7 wafers. Al0.58Ga0.42N was grown with the growth rate of 1.85μm/hr at 30 kPa. AlN was grown with the growth rate of 1.4μm/hr at 13kPa. AlN/GaN SLS (5nm/20nm) was also grown at the growth rate of 1.4μm/hr. An excellent uniformity of aluminum concentration of less than 0.5% was also obtained for Al0.58Ga0.42N. The challenge which we are facing to further increase of the throughput is summarized.

MOCVD growth of nitride semiconductors

Abstract In this chapter, specific characteristics of nitride semiconductor metal organic chemical vapor deposition are described about the following topics: growth mechanisms, Mg doping, visible multi quantum wellMQW growth, and ultraviolet materials growth by using high flow speed reactor. The importance of controlling vapor phase reaction is highlighted in view of growing low carbon materials for better electrical and optical properties as well as growing high aluminum content AlGaN alloys.

Characteristics of AlN layer on four-inch sapphire substrate by high-temperature annealing in nitrogen atmosphere

In this study, we developed an annealing furnace for 4 inch wafers and used it to anneal AlN on a 4 inch c-plane sapphire substrate at 1700°C for 1 h in a pure N2 atmosphere by using the annealing furnace (STA1800, Taiyo Nippon Sanso). FWHM of the XRC of the (0002) of 48.6 arcsec, and that of the (10-12) of 278.2 arcsec was obtained.

Improving the light output power of DUV-LED by introducing the intrinsic last quantum barrier interlayer on the high-quality AlN template

We demonstrate that the light output power of deep ultraviolet light emitting diodes (DUV-LEDs) can be improved by introducing the intrinsic last quantum barrier interlayer on the high-quality (HQ) AlN template. With the use of HQ AlN template, the light output power of 280 nm DUV-LEDs increases about 33 % which relative to the low-quality (LQ) ones. In addition, we found the light output power can be further enhanced to 3.15 mW by inserting the intrinsic last quantum barrier interlayer.

Relationship between Al content of AlGaN buffer layer on top of initial AlN nucleation layer on Si and vertical leakage current of AlGaN/GaN high-electron-mobility transistor structures

The vertical leakage current of AlGaN/GaN high-electron-mobility transistors on Si substrates was studied. The effects of the Al content in the AlGaN buffer layer and pit density on the vertical leakage current were not as significant as the effect of the initial AlN layers crystal quality.