Excited states of bound excitons in wurtzite‐type semiconductors

Abstract

Excitons bound to neutral impurities are studied with respect to excited states by means of excitation spectroscopy in CdS single crystals a t 1.8 K. The symmetry of the four excited states of the exciton bound to neutral donor (placed energetically below the free exciton) can be deduced from the observed dependence of their optical transitions on the direction of the wave vector and the polarization. Theoretical considerations taking into account the complex valence band structure of wurtzite-type semiconductors lead to an explanation of these states in terms of excited (p-and d-like) hole states of the bound exciton. With respect to the exciton bound t o neutral acceptor only the well-known I1B-states are found experimentally arising from the incorporation of a hole from the lower B-subvalence band in the complex. Mit Hilfe der Anregungsspektroskopie werden angeregte Zustiinde von gebundenen Exzitonen in

Excited states of neutral donor bound excitons in GaN

“…In addition, electronic excited states (blue) can be observed in both PL and PLE spectra, which correspond to the excited (e.g., p-and d-like) states of the hole in a D 0 X A center, as first described by Puls et al for excited D 0 X A states in CdS. 16 Similar to molecular vibrations, the four-particle complex of a D 0 X A center can also exhibit rotational and vibrational states (green), which are usually situated in close vicinity to the ground state. 1,13 As first pointed out by Thomas and Hopfield for bound excitons in CdS, 15 a clear experimental distinction between such electronic and rotational-vibrational excited states is not feasible as the electron and hole possess effective masses of the same order of magnitude-in clear contrast to the atomic/molecular case.…”

“…Depending on the anisotropy of the hole mass m h , the degeneracy of the electronic states with respect to the magnetic quantum number (m) is lifted, leading to, e.g., a twoor threefold splitting depending on the angular momentum quantum number l. 16 Normally, states with l ! 2 lie energetically above the X A transition and are therefore unstable.…”

“…(3) still exhibit a degeneracy in m, which is lifted as soon as the anisotropy of the effective hole mass in GaN is considered. Depending on the particular excited state jn r ; l; mi, a corresponding averaging of the perpendicular and parallel m h values must be considered, 16 which is additionally weighted by the ratio of the static dielectric constants for each such directions. 24 Interestingly, in the literature Eq.…”

“…24 Interestingly, in the literature Eq. (3) is employed in two different ways: (1) the total energy E b ð Þ is either fully minimized 31 (technically correct) or (2) E b ð Þ is just minimized until the experimentally observed ground state energy is reached, 13,16 while sometimes even D is used as an additional free parameter. 35 Based on our analysis from Sec.…”

Optical signature of Mg-doped GaN: Transfer processes

“…The third group of excitation channels are the electronic excited states of the exciton which can well reach energy spacings greater than e.g. the A-Bvalence band splitting in GaN and can be theoretically modeled following a formalism presented by Puls et al 69 for exciton complexes in CdS. We assume that excitonic complexes with orbital (radial) n r and angular momentum quantum number l in the range of 0 ≤ (n r , l) ≤ 2 are viable candidates for the observed excitation channel of ABX3 but the line width limitations of the excitation channels hinders a more detailed analysis.…”