Novel Method for the Activation of Acceptor Dopant in AlN Introducing Localized Band by Isoelectronic Dopant
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Novel Method for the Activation of Acceptor Dopant in AlN Introducing Localized Band by Isoelectronic Dopant Toshiyuki Takizawa Semiconductor Device Research Center, Semiconductor Company, Matsushita Electronic Industrial, Co., Ltd., 1-1 Saiwai-cho, Takatsuki, Osaka 569-1193, JAPAN
ABSTRACT In this study we propose a novel method to increase hole concentration introducing isovalent substitutional dopant into a p-type nitride semiconductor. Acceptor dopant in nitride semiconductors makes deep acceptor level (>100 meV) and generates few hole carriers into the valence band because of large electron affinity of N. In contrast to this, substitution of isovalent group-V atoms (P, As and Sb) that has smaller affinity than N makes a localized group-V band upward the valence band maximum (VBM). When both acceptor and isovalent group-V atoms are incorporated into nitride semiconductor, holes can be drastically activated by isovalent atoms, and can easily move in the group-V band. We have also investigated this material, Mg-doped AlN:V (V=P, As or Sb), using first-principles pseudopotential method. As a calculation result, substitiution of P and As makes localized group-V band upward the VBM of AlN, and moreover this can be adjusted the VBM of GaN. The Mg incorporation into AlN:V as an acceptor dopant drastically decreases the Fermi level (∆EF=-0.10 eV), that is, hole concentration can be drastically raised by the group-V band. Consequently novel p-type material with isovalent dopant can be a candidate to efficiently inject hole current into the VBM of GaN.
INTRODUCTION GaN and the related materials have recently gained attention because of its possible use in blue-green light-emitting diodes and blue-emitting laser diodes[1]. However, p-type doping problems remain one of the crucial issues for large-scale applications in the optical devices. The acceptor level of Mg-doped GaN is experimentally estimated to be more than 100 meV which value is too large to thermally excite hole carrier at the room temperature[2]. Several researchers have investigated the growth of p-type GaN, and have revealed that the residual hydrogen strongly relates to the activation of acceptor[3,4]. Various mechanisms to limit the hole concentration in p-type GaN have been reported[5]. Recently the codoping method has been proposed by T. Yamamoto et al[6], and has been successfully demonstrated[7]. On the other hand, P. Kozodoy et al have successfully increased hole concentration due to valence band bending induced by piezoelectric polarization in Mg-doped AlGaN/GaN superlattice structures[8]. The main purpose of this work is to propose the new method using an isovalent substitutional dopant[9,10] for obtaining high hole concentration in p-type wide-bandgap semiconductors. In this work, we first carry out the electronic band structure calculations
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of p-type doped AlN. Secondly, we investigate the effects of isoelectronic dopants actively codoped into p-type AlN materials.
PRINCIPLES Figures 1 (a) and (b) schematically show the cry
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