David B. Laks

Acceptor doping in ZnSe versus ZnTe

It is a long‐standing puzzle that ZnSe is difficult to dope p type, while ZnTe—which is very similar to ZnSe—is very easily doped p type. We report ab initio calculations which show that the solubilities of Li and Na acceptors are much greater in ZnTe than the solubilities of the same acceptors in ZnSe. We trace the origin of this difference to the bonding properties of the acceptors with the neighboring chalcogens. Our results also explain the experimentally observed dependence on dopant concentration of the dislocation density in p‐type ZnSe epilayers grown on GaAs.

Dependence of the optical properties of semiconductor alloys on the degree of long-range order

Many III‐V semiconductor alloys exhibit spontaneous [111] alternate monolayer ordering when grown from the vapor phase. This is manifested by the splitting of the valence‐band maximum and by a reduction in the direct band gap. We show here how these features can be used to deduce quantitatively the degree of long‐range order in a given sample. Examples are given for Ga0.5In0.5P and Ga0.5In0.5As alloys.

Doping limits in ZnSe

We explore doping problems in p-type ZnSe using ab initio total-energy calculations. Our method determines the formation energies of native point defects and of acceptor dopants as a function of the relative abundance of Zn, Se and the dopant atoms, resulting in a map of the concentrations of defects and dopants over the entire thermodynamically allowed range of conditions. For native point defects, which were often assumed to compensate the doping of ZnSe, we show that their concentrations are negligibly small over most of the range of allowed stoichiometry. For a ZnSe acceptor-doped with LiZn or NaZn, we find that compensation by Lii and Nai donors is possible, but can be avoided in a sufficiently Se-rich environment. The most stringent limits on acceptor doping of ZnSe come from the solubility limits of the three dopants. Our calculations show that NaZn has a very low solubility limit, with a much higher limit for LiZn, and the highest for NSe.

Nitrogen doping in ZnSe and ZnTe

Abstract We present a theoretical investigation and discussion of N doping in ZnSe and ZnTe, based on first-principles calculations. We find that the experimentally observed trend in doping efficiency can be attributed to the higher solubility of N in ZnTe. We also discuss the potential formation of complexes between the N acceptor and native defects, the change in lattice constant of ZnSe due to heavy N doping, and some problems associated with N as an acceptor dopant.

Solubilities, defect reactions and doping limits in ZnSe

We have developed a theoretical formalism to determine concentrations of native defects and impurities in semiconductors, and applied it to the problem of p-type doping in ZnSe. Limitations in the achievable hole concentrations are not due to native defect compensation. Two mechanisms are responsible: one is the competition between various substitutional and interstitial configurations, the other is the solubility limit imposed by formation of other phases. A comprehensive examination of Li, Na and N acceptors in ZnSe is presented.

Theory of defects, impurities, and doping in ZnSe

Abstract The formation of native defects and incorporation of dopant impurities in ZnSe are addressed from a first-principles point of view. Our calculations of the atomic and electronic structure yield explicit microscopic information about atomic positions, relaxation and bonding. Hyperfine parameters are computed, which can be directly compared with experimental data. Our formalism also produces concentrations of the various defects and impurities. One of our major findings is that native defects are not responsible for the doping difficulties in ZnSe. Investigations of Li, a potential p-type dopant, indicate that the achievable hole concentration is restricted in this case by the limited stability and solubility of Li on the substitutional acceptor site.

Diamond-like order in zinc-blende compounds

Abstract We show that the energy of substitutional randomization of atoms in zinc-blende compounds is surprisingly small. This suggests the existence of a new class of defects in these materials (“random aggregates”), which consist of regions of ≲ 10 atoms where the sites of the diamond lattice are randomly occupied by A or B atoms in place of the ordered AB crystal occupancy. The structural and electronic properties of these defects are outlined.

Self-Compensation and Doping Problems in ZnSe

We examine native-defect compensation, solubility limits, and dopant self-compensation in ZnSe. Our results are based on a formalism, using first-principles density-functional theory, that treats dopant atoms and native defects on an equal footing. For the case of acceptor doping of ZnSe with Li, we find that compensation due to interstitial Li donors and to native donor defects can be reduced to a tolerable level by carefully adjusting the growth conditions. A more serious impediment to Li doping comes from the solubility limit of Li in ZnSe.