Short- and long-range-order effects on the electronic properties of III-V semiconductor alloys

Abstract

First-principles and empirical pseudopotentials are used to study the effects of short-range and longrange atomic order on the electronic properties of III-V semiconductor alloys. The alloy structure with a given degree of long-or short-range order is modeled by two types of supercells: (a) Small (16 -32 atom) supercells are constructed in the fashion of the special quasirandom structures (SQS) used previously to simulate random alloys [A. Zunger et al. , Phys. Rev. Lett. 65, 353 (1990)]. Their electronic structure is treated via first-principles pseudopotential methods. (b) Large ( -1000 atom) supercells are found by a simulated-annealing technique which optimizes the atomic configuration until a given degree of short-range order is reproduced. The electronic structure is then determined using the empirical pseudopotential method. Statistical tests prove that the small cell SQS mimic the much larger supercells and thus provide an efficient means of studying the electronic band structure of disordered alloys in a non-mean-field approach. For the direct band gaps of ideally random Al& "Ga"As, Ga& In"P, and Al&, In As alloys, we find optical bowing parameters b=0.48, 0.46, and 0.52 eV, respectively. In the presence of short-range order in the form of cation clustering, we find the following: (i) Clustering elongates the Ga-P bond and shortens the In-P bond in Gao &Ino 5P and (ii) the optical bowing of the direct band gap is greatly enhanced. This leads to an indirect-gap to direct-gap crossover in Alo &Gao 5As with sufficient clustering. (iii) The band-gap reduction is accompanied by a localization of band-edge wave functions on certain types of clusters. The clusters act as "isoelectronic impurities" which localize states if their concentration (i.e., the degree of short-range order) is large enough. Electrons at the conduction-band minimum localize on the cations with lower s-orbital energies. The bandgap reduction and wave-function localization of alloys with short-range order is compared to the effects of long-range order, where the gap reduction is due to level repulsion between zone-folding conduction states. Numerical results are given for CuPt-type long-range order of A1GaAs2, GaInP"and A1InAs~. For complete ordering, the band-gap reduction relative to the random alloys are 0.36, 0.49, and 0.16 eV, respectively.

Polymorphous band structure model of gapping in the antiferromagnetic and paramagnetic phases of the Mott insulators MnO, FeO, CoO, and NiO

“…Instead of constructing the SQS by fitting to the analytically known random pair and many body correlation functions (see Appendix A), one can fit to independently measures or calculated correlation functions that incorporate SRO. 65 In conclusion, in the present study we find that the DFT+U method, which is a generalized Kohn-Sham approach reproduces the insulating character and on-site magnetic moments of the prototypical Mott insulators MnO, NiO, CoO, and FeO when applied to SQSs, which approximate closely the ensemble average over the random magnetic configurations. Table 1.…”

Natural oxides on air-exposed and chemically treated InGaP surfaces grown by metalorganic vapor phase epitaxy

“…In this regard, surface and interface issues are very important. However, the variety of surface atomic arrangement of InGaP due to the well-known sublattice ordering effects [1][2][3] and an As/P intermixing at the phosphide/arsenide interface 4,5 make the control of surfaces and heterointerfaces rather complicated and difficult. In actual device fabrication process, in addition, unexpected interfacial chemical reactions can take place during the formation process of metal-semiconductor and insulator-semiconductor interfaces, reducing the reproducibility of the device processing.…”

Surface Fermi-level position and gap state distribution of InGaP surface grown by metalorganic vapor-phase epitaxy

“…3,4 However, the mechanism of such passivation effects is not fully understood. In addition, a variety of surface atomic arrangements of InGaP due to the well-known sublattice ordering effects [5][6][7] make the control of surfaces and heterointerfaces rather complicated and difficult. Nevertheless, experimental confirmation on the electronic properties of ''free'' InGaP surfaces, in particular, densities and distributions of surface states, has been largely lacking.…”

“…From the PL peak energy, an ordering parameter, , was estimated to be 0.3, using a value of 2.01 eV for the band gap of a completely disordered InGaP lattice and a value of 0.471 eV for the maximum decrease of a band gap in a completely ordered lattice. 6,10 The XPS valence-band spectra of the air-exposed and HCl-treated InGaP surfaces are shown in Fig. 3.…”