Characteristics of GaN Schottky Diode Grown on Sapphire Substrate by MOCVD

Abstract

We report here the characterization of metalorganic chemical vapor deposition grown GaN layer on sapphire substrate with (0001) orientation (c-face). The 2.4-μm-thick GaN layer on sapphire substrate showed the specular surface morphology. The full width at half-maximum of X-ray double crystal rocking curve was 214 arcsec. Photoluminescence measurement at 4.2 K showed the emissions from the two free excitons (FE_A and FE_B), acceptor and donor bound excitons (ABE and I₂) and the first excited state of FE_A. The etch pit density (EPD) was measured using molten KOH etching was 2~4×10⁸ cm⁻². The electron mobilities from Hall effect measurement were 585 cm²/V·s for the electron concentration 1.1×10¹⁷ cm⁻³ at 300 K, and 1217 cm²/V·s for 2.4×10¹⁶ cm⁻³ at 77 K, respectively. The measured mobility values are much higher than the previously reported values. The fabricated Pt/Ti/Au Schottky diode on GaN layer revealed the ideality factor 1.04 and the barrier height 0.9 eV which was calculated from forward current-voltage characteristics. The reverse current was as low as 1 mA for the reverse voltage 100 V. The barrier height was also determined to be 1.4 eV from the capacitance-voltage measurement. The electron-beam induced current observations were performed on the fabricated GaN Schottky diode. The dark spot was observed and the dark spot density was estimated to be 2×10⁸ cm⁻², which was comparable to the EPD measured using molten KOH etching. GaN metal semiconductor field effect transistors (MESFETs) with 3-μm gate-length and 15-μm gate-width have also been fabricated on high-quality GaN single crystalline layer. Maximum transconductance 25 mS/mm and the drain-source current 210 mA/mm have been achieved for the GaN MESFET.