Mechanism of current leakage in Ni Schottky diodes on cubic GaN and Al x Ga 1-x N epilayers
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0892-FF13-04.1
Mechanism of current leakage in Ni Schottky diodes on cubic GaN and AlxGa1-xN epilayers D.J. As1, S. Potthast1, J. Fernandez 1, K. Lischka1, H. Nagasawa2, M. Abe2 1 University of Paderborn, Department of Physics, Warburger Str. 100, D-33098 Paderborn, Germany; 2 HOYA Advanced Semiconductor Technologies Co., Ltd., 1-17-16 Tanashioda, Sagamihara, Kanagawa 229-1125, Japan ABSTRACT Ni Schottky-diodes (SDs) 300 µm in diameter were fabricated by thermal evaporation using contact lithography on cubic GaN and AlxGa1-xN epilayers. Phase-pure cubic GaN and c-Al0.3Ga0.7N/GaN structures were grown by plasma assisted molecular beam epitaxy (MBE) on 200 µm thick free-standing 3C-SiC (100) substrates. The quality of the cubic group III-nitride epilayers was checked by high resolution X-ray diffractometry, atomic force microscopy and photoluminescence at room temperature and at 2 K. Large deviations from the thermionic emission transport were observed in the current voltage (I-V) behavior of these SDs. Detailed analysis of the I-V characteristics at 300 K and at low temperature showed that a thin surface barrier is formed at the Ni semiconductor interface. Thermal annealing in air at 200°C alters the composition of this thin surface barrier and reduces the leakage current by three orders of magnitude. The doping density dependence of breakdown voltages derived from the reverse breakdown voltage characteristics of c-GaN SDs is in good agreement with theoretically calculated values and follows the expected trend. From these experimental data a blocking voltage of higher than 600V is extrapolated for c-GaN films with a doping level of N D =5x1015 cm-3. INTRODUCTION In GaN-based electronic devices such as high-power high electron mobility transistors (HEMTs), high-power metal semiconductor field effect transistors (MESFETs) and UV-photodetectors Schottky contacts are key elements for realization [1]. For these devices the width of the Schottky contact depletion layer thickness has to be controlled precisely for optimum device operation. However, GaN based Schottky contacts suffer from abnormal large leakage currents under reverse bias [2], which strongly degrade gate control characteristics and increase power consumption. Different field emission (FE) models assuming a triangular Schottky potential [3], trap-assisted tunnelling [4], spatial variations of barrier heights [5] and the introduction of a thin surface barrier (TSB) [6] have been used to explain this leakage mechanism. Cubic GaN, although more difficult to grow, allows a 50% gain in FET performance in comparison to wurtzite GaN as proposed by 2D Monte Carlo device simulations of nitrides field effect transistors (FET) [7]. If the cubic group-III nitrides are grown in (001) direction spontaneous and piezoelectric polarization effects can be avoided at the interfaces and surfaces.
0892-FF13-04.2
The density of the two-dimensional electron gas (2-DEG) in cubic AlxGa1-xN/GaN heterostructures will be independent on the thickness and Al mole fraction of the AlxGa
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