Resonant Raman scattering at bound excitons in ZnSe/GaAs epilayers

Abstract

We determine the electronic structure of t h e dominant donor-exciton complex (Do, X) in high-quality ZnSeIGaAs epilayers grown by molecular beam epitaxy. Besides the recombination line i2 from the ground state of t h i s complex, a set of further lines, called 12i (i = a , . . . , e), was observed in luminescence and excitation spectroscopy. They represent transitions into (or from) excited states (Do, X):of the same exciton complex which are described by single-hole excitation with different hole quantum numbers n , 1. Additionally, strong resonant electronic Raman scattering (RRS) occurs at these donor-bound exciton states. Several scattering lines S,; with non-constant Stokes shifts are identified as involving (DO, X) complexes with varying binding energies as resonant intermediate states. This phenomenon is explained by the strain influence in ZnSeIGaAs for different layer thicknesses, although t h e incorporation of different donor impurities may also contribute to t h e variations of the Stokes shifts

Optical properties of II-VI epitaxial layers

“…Looking for I;, which is controversially discussed as a heavy-hhle component of I,, or as transition from or into an excited electronic (Do, X) state (see comments to figure 2): its energy distance to I, amounts to 2.00meV in the MBE and 2.82 meV in the HWE sample, compared with the X,,-X,, distances of 3.28 and 4.95 meV, respectively. Thus, while the energy separation of I, from X,, is constant in both All other IZi lines are satisfactorily explained as transitions from or into excited electronic states of the (Do, X) system, as was explained earlier and is discussed in [3]. However, it is worth mentioning that their relative binding energies with respect to XI, vary drastically if the growth temperature is changed.…”

“…as well as the weak maxima magnetic field from the (Do, X) j = 1/2 and 3/2 degenerate zero-field ground state levels [5, 71. This aspect will he further discussed in [3] in connection with very recent Raman data at the (Do, X) complex. Figure 3 showing an excitation spectrum of I, demonstrates that in this kind of spectroscopy not only I,, to I;.…”

“…are seen on the I, high-energy side hut a complete set of seven resonances I,, being specific for I, [3, 111. The nature of these maxima will be discussed in terms of excited single-hole states of the (D$ X) complex (i.e. an excitation of the single hole within the system while the two electrons remain in their single-particle ground states) in [3].…”

“…The occurrence of high-density phenomena such as biexciton creation, carrier collision processes and electron-hole plasma formation will be sketched under the specific conditions of strained epitaxially grown thin films. Aspects of scattering phenomena in these films allowing for a scan over strain profiles and exciton-impurity binding energies are extensively discussed in another paper [3].…”

Exciton Electroluminescence of ZnSe/ZnO Structures under Biaxial Stress

“…The valence band at the Γ point of the unstrained ZnSe crystals consists of a fourfold degenerate P3/ 2 valence band (J = 3/2, m = ±3/2, m = ±1/2). Under biaxial compressive or tensile stress this valence band splits into a light-hole (J = 3/2, mj = f 1/2) and a heavy-hole (j = 3/2, m = ±3/2) branches [3][4][5]. The trend in II-VI compounds is that the materials have a larger negative deformation potential as their lattice constants get smaller.…”