A Study of Elemental Interdiffusion in GaN/Si Wafer Grown by Metalorganic Vapor Phase Epitaxy
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A Study of Elemental Interdiffusion in GaN/Si Wafer Grown by Metalorganic Vapor Phase Epitaxy X. Chen, M. Ishiko, Y. Kuroiwa1, and N. Sawaki1 Toyota Central R&D Labs. Inc., Nagakute, Archi, 480-1192, Japan 1 Department of Electronics, Nagoya University, Chikusa-ku, Nagoya, 464-8603, Japan ABSTRACT Secondary ion mass spectrometry (SIMS) study shows that a short-time interdiffusion process occurs at the interface of buffer/Si in the GaN/Si wafers grown by metalorganic vapor phase epitaxy (MOVPE). Increasing the growth temperature of the buffer layer from 11500C to 12100C reduces the dropping rate of Al concentration in the silicon substrate from ~20nm/decade to ~30nm/decade near the interface. The impact of the interdiffusion on the band structure is investigated by photocurrent spectroscopy measurement. The experimental results indicate that different build-in electric fields are formed in the GaN/n-Si(111) and GaN/p-Si(111) devices as the consequence of the MOVPE growth. INTRODUCTION Recent progress in AlGaN-based Schottky and p-i-n rectifies fabricated on heteroepitaxial layers on sapphire (Al2O3) substrates have shown reverse blocking voltages up to 9.7 kV on lateral structures[1]. While these results are impressive, the poor thermal conductivity of sapphire (κ=0.5 W/cm K) and the employed thin epilayer limit the current density in lateral devices. To overcome these limitations, devices, in which the current flows vertically, are proposed for power applications. Being conducting material, both SiC and Si have been used as alternative substrates to sapphire. But SiC cost is orders of magnitude higher than Si. It does not offer us a clear commercialization pathway while Si substrate not only supplies good electrical and thermal conductivity, but also allows for future integration of well established Si electronics. Moreover, crack-free, thick (~3 µm) GaN grown on large-area silicon wafers was reported recently[2,3]. Therefore, using Si as the substrate for fabrication of power devices with vertical contacts is an attractive subject. Due to the reaction between the Ga and Si substrate, a GaN film grown directly on the silicon substrate has very poor surface morphology and bad crystal quality. Employing an Al contained film as the nucleation layer deposited prior to GaN decreases the Ga concentration adjacent to the substrate and makes 2D growth of high quality GaN film on Si be available[4,5]. But, how
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the nucleation layer is initially formed is not completely cleared, yet. Here we present the investigation on the epitaxial interface in the GaN/Si wafer based on the secondary ion mass spectroscopy (SIMS) and the photocurrent spectroscopy measurement. EXPERIMENT All samples used in this study were fabricated on n- or p-type Si(111) substrate patterned by SiO2 into a grid style with a window area 300×300 µm2 and a mask width 20 µm. The crystal growth was operated in a horizontal MOVPE system at atmospheric pressure. A nominally 50nm thick buffer layer was first grown on the Si substrate, followed
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