Luminescence of CuInS2

We show for ZnO a correlation between the ionized donor bound exciton ${D}^{+}X$ recombinations ${I}_{0}$, ${I}_{1}$, and ${I}_{2}$ and the neutral donor bound exciton ${D}^{0}X$ recombinations ${I}_{6a}$, ${I}_{8}$, and ${I}_{9}$, respectively. The experimental data on the localization energies of ionized and neutral donor bound excitons are compared to theoretical predictions and a good agreement is found. We give an estimate of the localization energies of neutral acceptor bound excitons. One can conclude that the localization energies of neutral donor and acceptor bound excitons in ZnO will be very close in energy and an assignment of transition lines to donors and/or acceptors (in the absence of decisive data from magneto-optics) will not be straightforward.

Ionized and neutral donor-bound excitons in ZnO

Free and bound excitons have been studied by photoluminescence in thin () wurtzite-undoped GaN, n-type GaN:Si as well as p-type GaN:Mg and GaN:Zn layers grown by metal-organic chemical vapour phase deposition (MOCVD). An accurate value for the free A exciton binding energy and an estimate for the isotropically averaged hole mass of the uppermost valence band are deduced from the data on undoped samples. The acceptor-doped samples reveal recombination lines which are attributed to excitons bound to and respectively. These lines are spectrally clearly separated and the exciton localization energies are in line with Haynes' rule. Whenever a comparison is possible, it is found that the exciton lines in these thin MOCVD layers are ultraviolet-shifted by 20 to 25 meV as compared to quasi-bulk () samples. This effect is interpreted in terms of the compressive hydrostatic stress component which thin GaN layers experience when grown on sapphire with an AlN buffer layer.

Free and bound excitons in thin wurtzite GaN layers on sapphire

Luminescence of CuInS2: II. Exciton and near edge emission

Surface excitons in ZnO crystals

Binding energies, interparticle distances, oscillator strengths, and exchange corrections are calculated for the three-particle complex corresponding to an exciton bound to an ionized donor. The results are given as functions of the mass ratio of the electron and hole. Binding of the complex is obtained for mass ratios up to 0.426. The interparticle distances are up to 50 times larger than the corresponding exciton radius. The oscillator strengths are about ${10}^{4}$ times greater than those of free excitons, while the exchange corrections for the complex are comparable to those of free excitions. The results are applied to CdS and ZnO and compared with experimental results on these.

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W. Gorzkowski

Papers

Properties of Excitons Bound to Ionized Donors