Effects of energy-spectrum broadening in alloyed semiconductor superlattices

Abstract

The density of energy states is calculated for alloyed semiconductor superlattices for different excitation levels with cllowance for the effects of screening and fluctuatio.zs of impurity -oncentrations. The influence of the state density tails on spontaneous-emission spectra is investigated for cross-over transitions and in a model without a selection rule for the electron wave vector. Account for the state density tails allows one to describe the longwave wing and shape of spontaneous-emission spectra in accordance with experimental data.

Hydrogen implantation effect on optical properties of GaAs doping superlattices

“…As modeling shows [11], the tunable PL band maximum hω PL coincides with the difference of the quasi-Fermi levels ∆F, which in turn is close to the effective energy gap g E′ of DSL at low temperatures. Even though the power of laser excitation P was not relatively high, the value hω PL of the tunable PL band reached 1.44 eV at P = 0. .…”

“…This can be observed most clearly at low temperatures in the quantum limit conditions [12]. Using the procedure described elsewhere [11], we obtain for the broadening parameters of the density state tails in the conduction and valence bands . By possible doubling of the acceptor concentration N a due to the hydrogen implantation, the parameter σ c does not practically change but the value of σ v decreases negligibly (≈ 17 %).…”

“…Here, the modeling takes into account the effects due to fluctuations of the impurity concentration. For the broadening parameters σ c and σ v of the density state tails, we can use the values that include the effect of correlation impurity screening [11]. Under excitation of DSLs the screening length shortens, which has an influence on the energy tail distribution and on the population in the subbands.…”

“…where all the parameters have their usual meaning [10][11][12]. A similar expression with the corresponding parameters (m vi , E vinν , σ v , F h ) can be written for the concentration of heavy and light holes (i = h, l) in the subbands of p-layers.…”

Nonlinearities in the reflection and transmission spectra of the photonic bandgap heterostructures with n–i–p–i crystals

“…The nonlinear processes in the n-i-p-i superlattices are connected with (a) the filling or emptying of the energy states under optical excitation of the crystal, (b) redistribution of the energy levels at changing the potential relief depth, (c) the shortening of the density state tails, which are related to the impurity concentration fluctuations, at the screening of the electrostatic potential by nonequilibrium current carriers, (d) change in the lifetime of current carriers due to changes in the overlap of the envelope wave functions of electrons and holes, (e) masking behavior of the free carrier absorption, (f) stabilizing action of the background screening, (g) saturation of absorption or amplification, and (h) effects of narrowing the semiconductor band gap and of changing the effective band gap of the superlattice (Kononenko et al 1998;Ushakov et al 1999Ushakov et al , 2001.…”