Band offsets of semiconductor heterostructures: A hybrid density functional study

Abstract

We demonstrate the accuracy of the hybrid functional HSE06 for computing band offsets of semiconductor alloy heterostructures. The highlight of this study is the computation of conduction band offsets with a reliability that has eluded standard density functional theory. A high-quality special quasirandom structure models an infinite random pseudobinary alloy for constructing heterostructures along the (001) growth direction. Our excellent results for a variety of heterostructures establish HSE06's relevance to band engineering of high-performance electrical and optoelectronic devices.PACS numbers: 78.55.Cr Heterostructures are ubiquitous in semiconductor technology.For instance, AlInAs/InGaAs is used for quantum cascade lasers and infrared photodetectors; InGaP/AlGaAs for high electron mobility transistors (HEMTs), heterojunction bipolar transistors (HBTs), and phototransistors; AlInAs/InP for HEMTs; In-GaP/GaAs for HBTs; and InGaAs/InP for single-photon avalanche photodiodes and HBTs. Among the most important properties that determine the feasibility and performance of heterostructure devices are the band offsets. These are the discontinuities between the valence band maxima (VBM) or conduction bands minima (CBM) of each semiconductor at their common interface, and act as barriers to electrical transport across the interface. Band engineering of novel devices with desired properties, particularly quantum cascade lasers and quantum dot-based devices, critically require a precise knowledge of band offsets. However, reliable measurements and predictions of band offsets continue to be challenging despite extensive theoretical and experimental efforts. [1][2][3] Density functional theory (DFT) is an efficient method for calculating electronic structure. The accuracy of DFT calculations is controlled by the choice of exchangecorrelation (XC) functional. Local and semi-local functionals such as LDA (local density approximation) and PBE (Perdew-Burke-Ernzerhof) 4 fail to produce accurate bandgaps, and in extreme cases predict small gap semiconductors as metals. Hybrid XC functionals, that include a fraction of Hartree-Fock (HF) exchange, provide a promising alternative. In this letter, we determine the suitability of a hybrid functional HSE06 (Heyd-Scuseria-Ernzerhof) 5 to compute band offsets of several III-V compounds and pseudobinary alloy heterostructures. HSE06 includes a fraction, α, of screened, shortrange HF exchange to improve the derivative discontinuity of the Kohn-Sham potential for integer electron numbers (default HSE06 uses α=0.25). This functional was recently used to predict the band alignments throughout a) 1.52 (ind) 0.21 1.12 0.18 mod−HSE06 Experiment PBE 2.10 (ind) 0.27 0.31 1.52 2.19 (ind) 0.26 0.42 1.52 FIG. 1. Band alignments for Al0.5Ga0.5As/GaAs heterostructure computed with mod-HSE06 (α = 0.30, see text) and PBE, in comparison with experiment. 2 The direct and indirect bandgaps are shown for GaAs and Al0.5Ga0.5As, respectively. The hybrid functional shows significant improvement over PBE ...

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