Highly doped p-type a-plane GaN grown on r-plane sapphire substrate
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0892-FF17-06.1
Highly doped p-type a-plane GaN grown on r-plane sapphire substrate Y. Tsuchiya, Y. Okadome, H. Furukawa, A. Honshio, Y. Miyake, T. Kawashima, M. Iwaya, S. Kamiyama, H. Amano and I. Akasaki Faculty of Science and Technology, 21st-Century COE Program “Nano-Factory”, Meijo University, 1-501 Shiogamaguchi, Tempaku-ku., Nagoya 468-8502, Japan e-mail: [email protected] ABSTRACT Mg-doped p-type a-plane GaN films were grown on unintentionally doped a-plane GaN templates by metalorganic vapor phase epitaxy (MOVPE). The Mg concentration in a-plane GaN increased with increasing Mg source gas flow rate. A maximum hole concentration of 2.0 × 1018 cm-3 with a hole mobility of 4.5 cm2/Vs and resistivity of 0.7 Ω･cm were achieved. The activation ratio was 5.0 × 10-2. It was found that a maximum hole concentration in p-type a-plane GaN was higher than that in p-type c-plane GaN. The activation energy of Mg acceptors in p-type a-plane GaN with the maximum hole concentration was found to be 118 meV by temperature-dependent Hall-effect measurement. INTRODUCTION Major breakthroughs
such
as
the
improvement
of
crystalline
quality
by
a
low-temperature-deposited (LT-) buffer layer technique [1] and the realization of conductivity control of nitrides [2-4] have lead to high-performance violet- and blue-light-emitting diodes (LEDs) based on the c-plane group III nitrides. However, conventional c-plane multiple quantum well (MQW) structures generate fixed sheet charges at the heterointerfaces due to polarization discontinuities. The large piezoelectric polarization in group III nitride heterostructures results in built-in electrostatic fields that lead to the spatial separation of electron and hole wave functions in the quantum well, redshifted emission, and an overall reduction in the radiative recombination efficiency [5,6]. Recently, several groups have studied nonpolar-plane (such as a-plane GaN grown on an r-plane sapphire substrate) nitride-based optoelectronic devices [7,8]. However, the performance of LEDs on r-plane sapphire is still inferior to those of LEDs grown on c-plane sapphire. In addition to the poor crystalline quality, the lower hole concentration of less than 7.0 × 1017 cm−3 at room temperature (RT) in p-type a-plane GaN [8] poses serious problems to the realization of high-performance LEDs. The growth of high-quality a-plane GaN is essential for achieving p-type a-GaN with a high hole concentration. In this study, high hole concentrations of p-type a-plane GaN were achieved by growing it on high-crystalline-quality a-plane GaN. Temperature-dependent Hall-effect measurement and
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photoluminescence (PL) measurements were performed. EXPERIMENTS The Mg-doped p-type a-plane GaN grown
on
high-crystalline-quality a-plane GaN templates using +0.5°-off r-plane sapphire substrates [9] and inserting AlGaN
and
AlN
[10].
Trimethylaluminum trimethylgallium (TMG),
(TMA), ammonia
(NH3) and ethyl-bis-cyclopentadienyl
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2.0x10 RT 1
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