High Barrier Height n-GaN Schottky diodes with a barrier height of 1.3 eV by using sputtered copper metal

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ABSTRACT Copper Schottky diodes on n-type GaN grown by metal-organic chemical vapor deposition were achieved and investigated. Ti/Al was used as the ohmic contact. The copper metal is deposited by the Sputter system. The barrier height was determined to be as high as (B =1.13eV by current-voltage (I-V) method and corrected to be IB =1.35eV as considered the ideality factor, n, with the value of 1.2. By the capacitance-voltage (C-V) method, the barrier height is determined to be 1 B =1.41eV. Both results indicate that the sputtered copper metal is a high barrier height Schottky metal for n-type GaN. INTRODUCTION GaN-based materials have been intensively studied recently for the blue emission diodes. Besides that, they have the potential in the applications of high temperature, high frequency and high power electronic devices due to its wide band gap and chemical stability characteristics. For some electronic devices like MESFET, it is necessary to fabricate a Schottky contact with a high breakdown voltage and a low reverse leakage current, up to a high reverse voltage. The metals with high work functions have been reported by many researchers to be used as a Schottky contact for GaN1 9 ). In this study, the Cu metal deposited by the sputter system was used as a Schottky contact to fabricate a Cu/n-GaN Schottky diode. The Schottky barrier height of the copper metal for n-GaN grown on the A120 3 substrate was investigated by using the I-V and C-V measurements.

523 Mat. Res. Soc. Symp. Proc. Vol. 572 © 1999 Materials Research Society

EXPERIMENT The samples used for this study were grown by the low pressure metal-organic vapor phase epitaxy (MOVPE) system. Trimethylgallium (TMGa) and NH3 were used as source materials, and SiH4 diluted in H2was used as the n-type dopant source. The sapphire substrate was first heated at 1100IC for 20min in the stream of H2. A 25nm thick GaN layer was deposited as the buffer layer at 525°C. Then, the substrate was heated up to 1050'C and a 2gm thick Si doped GaN layer was grown on the GaN buffer layer. The carrier concentration of the Si doped GaN film was 5xl0' 7cm3 measured by the Hall measurement. The GaN samples were first cleaned with organic solvents, followed by etching in a HCl:H 20 solution, and then were loaded in an E-gun evaporator equipped with the cryo pump. Ti (50nm) and Al (100nm) were evaporated using the conventional lift-off technique. After lift-off process, the sample was annealed at 550'C for 5min in nitrogen ambient in order to obtain ohmic characteristics. Then, Cu (100nm) was deposited on the GaN film by sputtering and the pattern of the Cu contact was formed by using the wet etching with a solution of 10% HNO 3. Prior to the sputtering process, the sample was cleaned in boiling aqua regia for 5 min and dipped in HCl:H 20 for 1min. The area of the Schottky contact was 9.5xl0.5 cm2. The current-voltage (IV) and capacitance-voltage (C-V) characteristics were measured with HP4145 semiconductor parameter analyzer and Keithly 590 C-V analyzer. RESULT AND DISCUSSION