Abstract
p-Type doping represents a key step towards III-nitride (InN, GaN, AlN) optoelectronic devices. In the past, tremendous efforts have been devoted to obtaining high quality p-type III-nitrides, and extraordinary progress has been made in both materials and device aspects. In this article, we intend to discuss a small portion of these processes, focusing on the molecular beam epitaxy (MBE)-grown p-type InN and AlN—two bottleneck material systems that limit the development of III-nitride near-infrared and deep ultraviolet (UV) optoelectronic devices. We will show that by using MBE-grown nanowire structures, the long-lasting p-type doping challenges of InN and AlN can be largely addressed. New aspects of MBE growth of III-nitride nanostructures are also discussed.
Highlights
Compared to III-V compound semiconductors, one unique feature of III-nitrides is the widely tunable direct bandgap energies from ~0.64 to 6.2 eV, corresponding to ~1.9 μm to 200 nm in wavelength, which essentially covers near-infrared, visible, and deep UV [1]
Review recent advances on Mg-doped InN and AlN nanowire structures grown by molecular beam epitaxy (MBE), including direct evidence p-type doping in Mg-doped nanowires high free hole
These achievements in p-type doping are attributed to by MBE, including direct evidence for p-type doping in Mg-doped InN nanowires and high free hole concentrations in Mg-doped AlN nanowires
Summary
Compared to III-V compound semiconductors, one unique feature of III-nitrides is the widely tunable direct bandgap energies from ~0.64 to 6.2 eV, corresponding to ~1.9 μm to 200 nm in wavelength, which essentially covers near-infrared, visible, and deep UV [1]. P-type Al-rich AlGaN alloys can be obtained; the free hole concentration is generally very low [29,30,31,32,33,34,35,36,37,38], mainly limited by the large Mg activation energy (~600 meV) in the end compound AlN [31,39]. For p-type AlN the reported free hole concentration is only on the order of 1010 cm−3 [39] Besides this fundamental physical limitation, from the materials growth point of view, the compensation of Mg dopants and Mg desorption at the high growth temperature for Al-rich AlGaN alloys, in particular for MOCVD grown samples, limit the maximum available Mg dopants for free hole generation.
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