Computational Materials Science, an Increasingly Reliable Engineering Tool: Anomalous Nitride Band Structures and Device Consequences

Abstract

Computational materials science has evolved in recent years into a reliable theory capable of predicting not only idealized materials and device performance properties, but also those that apply to practical engineering developments. The codes run on workstations and even now are fast enough to be useful design tools. A review will be presented of the current status of this rapidly advancing field. Examples of the accuracy of the codes are displayed by comparing the predicted atomic volumes, and cohesive and excess energies of several materials with experiment. As a further demonstration of the methods, the band structures of AlN, GaN, and InN in wurtzite and zinc blende structures will be presented. There are anomalies in the conduction and valence bands of these materials. Some consequences on light emitting and power devices made from these materials will be examined.

Band gap and band parameters of InN and GaN from quasiparticle energy calculations based on exact-exchange density-functional theory

“…Subsequent G 0 W 0 calculations only open the gap to 0.02-0.05 eV, 12,13 while adding self-interaction corrections to the DFT calculations, either in the screenedexchange approach, 6 exact-exchange optimized effective potential ͑OEPx͒ approach, 14 or self-interaction corrected ͑SIC͒ LDA approach, 15,16 yields a semiconductor with band gaps of 0.8, 1.0, and 1.6 eV for the wurtzite phase, respectively. Here we apply the G 0 W 0 corrections to OEPx ground state calculations, which are fully self-interaction-free.…”

“…[3][4][5][6][7] Different hypotheses have been proposed to explain the large variation in the measured band gaps. Defects could be responsible for inducing states in the band gap or give rise to a pronounced Burnstein-Moss effect due to a shift in the Fermi level caused by a high intrinsic electron density.…”

Consistent set of band parameters for the group-III nitrides AlN, GaN, and InN

“…26 They proceeded to "remedy that obsolescence, by providing a completely revised and updated description of the band parameters for nitride-containing semiconductors" in 2003. 26 While this update includes evidence supporting a revision of the band gap of InN from its former value of 1.9 eV to a significantly lower value around 0.7 eV, [28][29][30][31][32] they had to concede that in many cases experimental information on certain parameters was simply not available. 26 This was mostly due to growth-related difficulties in producing high-quality samples for an unambiguous characterization.…”

Nitrogen vacancies in InN: Vacancy clustering and metallic bonding from first principles

“…In particular, even the fundamental physical parameters of InN are still under debate: e.g., there has been recent controversy over the band gap of InN, i.e., whether it is around 1.9 eV, as has been widely accepted, 4,5 or closer to 0.7-0.8 eV, as has been experimentally reported [6][7][8] and obtained from recent first-principles calculations. [9][10][11] Although some recent experiments 12 report a somewhat larger value of 1.4 eV, ab initio calculations in the literature give a wide range of values for the band gap of wurtzite InN depending on the following description: all-electron and pseudopotential calculations including the In 4d electrons yield a tiny, no, or negative band gap; 8,13 self-interaction and relaxation corrected pseudopotential calculations give 1.55 eV; 14,15 GW calculations yield 0.02 eV; 8 and a value of ϳ1.4 eV was estimated by using the exact-exchange ͑EXX͒ approach. 16 Screened exchange local-density approximation ͑LDA͒ calculations report band gaps of 0.8 eV ͑Ref.…”