When group-III nitrides go infrared: New properties and perspectives

Abstract

Wide-band-gap GaN and Ga-rich InGaN alloys, with energy gaps covering the blue and near-ultraviolet parts of the electromagnetic spectrum, are one group of the dominant materials for solid state lighting and lasing technologies and consequently, have been studied very well. Much less effort has been devoted to InN and In-rich InGaN alloys. A major breakthrough in 2002, stemming from much improved quality of InN films grown using molecular beam epitaxy, resulted in the bandgap of InN being revised from 1.9 eV to a much narrower value of 0.64 eV. This finding triggered a worldwide research thrust into the area of narrow-band-gap group-III nitrides. The low value of the InN bandgap provides a basis for a consistent description of the electronic structure of InGaN and InAlN alloys with all compositions. It extends the fundamental bandgap of the group III-nitride alloy system over a wider spectral region, ranging from the near infrared at ∼1.9 μm (0.64 eV for InN) to the ultraviolet at ∼0.36 μm (3.4 eV for GaN) or 0.2 μm (6.2 eV for AlN). The continuous range of bandgap energies now spans the near infrared, raising the possibility of new applications for group-III nitrides. In this article we present a detailed review of the physical properties of InN and related group III-nitride semiconductors. The electronic structure, carrier dynamics, optical transitions, defect physics, doping disparity, surface effects, and phonon structure will be discussed in the context of the InN bandgap re-evaluation. We will then describe the progress, perspectives, and challenges in the developments of new electronic and optoelectronic devices based on InGaN alloys. Advances in characterization and understanding of InN and InGaN nanostructures will also be reviewed in comparison to their thin film counterparts.

Understanding the role of Si doping on surface charge and optical properties: Photoluminescence study of intrinsic and Si-doped InN nanowires

“…It can be seen that there exist two distinct slopes, which change at ∼ 100 K (about ∼ 8 meV); this slope change temperature sets an upper limit of the exciton binding energy, [53][54][55] which is consistent with the previously reported value ∼ 9 meV from Wu et al. 18 Additionally, the exciton binding energy is suggested to be related to the activation energy derived in the low temperature range (10 to 100 K), 56,57 which is ∼ 3 meV in this study. This small activation energy is consistent with the derived exciton binding energy ∼ 2 − 3 meV if assuming InN dielectric constant ǫ ∼ 14, and effective mass for electron m * e = 0.05m 0 and for hole m * h = 0.3m 0 .…”

“…10,18 As shown in Fig and PL spectra measurements in InN films, 5,10,18,52 suggesting the nature of this PL emission is band-to-band carrier recombination. This result is in direct contrast to the nearly temperature invariant PL emission characteristics of n-type degenerate InN nanowires.…”

“…18 . This nearly linear I − P dependence further confirms that the emission is directly related to free-exciton recombination at low temperatures.…”

“…[16][17][18] To date, however, the practical device applications of InN-based materials have been severely limited by the presence of extremely large residual electron density and the uncontrolled surface charge properties, as well as the difficulty in achieving p-type conductivity. 8,[19][20][21][22][23][24][25][26][27][28][29][30] For example, in general, the currently reported nominally undoped InN is n-type degenerate, with the residual electron densities in the range of ∼ 1 × 10 18 cm −3 , or higher.…”

Characterization of InGaN/GaN quantum well growth using monochromated valence electron energy loss spectroscopy

“…The technology based on AlN, GaN, and InN as well as their ternary and quaternary compounds has been successfully implemented in a wide range of applications in both optical and electronic devices, which are operated at high temperatures, high frequencies, and high power. [1][2][3][4] GaN-based heterostructures like InGaN/GaN single or multiple quantum wells (QWs) dimensioned on the nanoscale are employed as the active layer in high-brightness light emitting diodes, laser diodes, and multi-junction solar cells with high internal quantum efficiencies. 5,6 The direct bandgap of InGaN allows for tunable color emission, covering the whole visible and parts of the ultraviolet and infrared spectral ranges.…”