We present a comparison of theoretical calculations and experimental measurements of the Auger recombination rate in a narrow-gap semiconductor superlattice with a complex band structure. The calculations and measurements indicate that the rate depends on density as n 2 for low density, and changes to an n dependence when the electrons and holes become degenerate. The calculations are the first to incorporate superlattice umklapp processes, which contribute about half of the total rate and substantially improve the agreement with experiment.
The spin-splitting energies of the conduction band for ideal wurtzite materials are calculated within the nearest-neighbor tight-binding method. It is found that ideal wurtzite bulk inversion asymmetry yields not only a spin-degenerate line ͑along the k z axis͒ but also a minimum-spin-splitting surface, which can be regarded as a spin-degenerate surface in the form of bk z 2 − k ʈ 2 =0 ͑b Ϸ 4͒ near the ⌫ point. This phenomenon is referred to as the Dresselhaus effect ͑defined as the cubic-ink term͒ in bulk wurtzite materials because it generates a term ␥ wz ͑bk z 2 − k ʈ 2 ͒͑ x k y − y k x ͒ in the two-band k • p Hamiltonian.
Temperature and density-dependent Auger recombination rates are determined for a four-layer broken-gap superlattice designed for suppression of both Auger recombination and intersubband absorption. The structure is intended as the active region of both optically pumped and diode lasers operating in the midwave infrared. Auger recombination and intersubband absorption are thought to be among the primary factors contributing to high-threshold current densities in such devices. Ultrafast time-resolved photoluminescence upconversion was used to measure the Auger rates at lattice temperatures ranging from 50 to 300 K. Results are compared to calculated rates using the temperature-dependent, nonparabolic K-p band structure and momentum-dependent matrix elements. The calculations, which include umklapp processes in the superlattice growth direction, are in excellent agreement with the experimental results. Comparison of these results with those obtained in other mid-IR semiconductor structures verifies Auger suppression. The measured temperature-dependent Auger recombination rates, together with calculations of the gain, provide an upper bound for the characteristic temperature, T 0 ϭ81 K, for lasers utilizing this superlattice as an active region.
The energy relaxation of InN thin films has been studied by ultrafast time-resolved photoluminescence technique. The obtained carrier cooling curves can be explained by carriers releasing excessive energy through the carrier–LO-phonon interaction. The extracted effective phonon emission times decrease as the photoexcited carrier concentration reduces and come close to the theoretical prediction of 23fs at small carrier concentration. The reduction of energy loss rate at high photoexcited carrier density is attributed to the hot phonon effect.
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