K. Unger

Spontane und induzierte Emission in Laserdioden@@@Spontaneous and stimulated emission in junction lasers: II. Bercksichtigung der Zustandsdichteschwnze@@@II. Bands with state density tails

The threshold current calculation of part I is extended to include the effect of the state density tails. We use the model suggested byKane and take tails for the conduction and valence band of equal characteristic energies. Under a certain approximation for the shape of the tails it is possible to derive an explicite threshold current formula, which takes into account the influence of the impurity concentrations without adjustable parameters. The comparison with experimental data for GaAs junction lasers gives favourable results.The laser photon energy dependence on resonator lost is calculated, this gives a tool to estimate the impurity concentration in the active region.A new approach to calculate threshold currents of semiconductor lasers for the model without any k-selection rule ofLasher andStern is presented. For parabolic bands and an active region of given width we derive an explicite threshold current formula, which gives j∼T3 for high temperatures (T>100 °K) and only small temperature dependence of j for low temperatures. The essential approximation involved is to replace the parabolic state density by a box-like state density of equal total carrier population. The active region is taken at a position, where the gain reaches its maximum value. Applications to GaAs-lasers — especially saturation effects — are discussed.

Disorder-induced intervalley scattering rates of AlxGa1-xAs by empirical pseudopotential calculations

The probability rates for transitions between different states of the virtual crystal induced by a random distribution of the cations in the ternary alloy system AlxGa1-xAs are calculated in the Born approximation using local empirical pseudopotentials, which are consistent with newer Eg(x) data and always yield the same arsenic potential. Attention is paid to scattering between the inequivalent conduction band valleys at the high-symmetry points Gamma , X and L for material near the transition from direct to indirect band structure (cross-over), which is of importance for application to the dynamics of excited carriers in optical switching and memory devices. In order to describe the net rate of electron transfer between two valleys 1 and 2 by integral S12g1g2(f1-f2) dE, where g(E) and f(E) are the corresponding densities of states and distribution functions respectively, the scattering factor S12 and its energy dependence is obtained exactly by averaging individual transition matrix elements over all energetic resonant states belonging in each case to 1 or 2. In this connection we give for the first time theoretical values for the strength of disorder-induced X-L coupling and present energy-dependent time constants tau 12=(S12(g1+g2))-1, concerning the occupation-probability relaxation by disorder-induced intervalley scattering.

Decay kinetics and phase behaviour of a dense carrier system in GaP:N

Abstract The densities and decay times of the two coexisting phases in highly-excited nitrogen-doped GaP are determined. Special attention is directed to a possible alteration of the spectra due to stimulated emission. The time behaviour is influenced by a flow of carriers into the liquid corresponding to a negative pressure. From the decay times the coefficients of the radiative and nonradiative transitions are determined.