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.

No abstract

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.

We have used the 830 nm, subpicosecond output of a mode-locked Ti:sapphire laser, together with subpicosecond 3.55 m pulses from a synchronously pumped optical parametric oscillator, to perform room-temperature, time-resolved, differential transmission measurements on a multiple quantum well structure with AlGaSb barriers and GaInSb/InAs superlattice wells. From these measurements, we have determined a Shockley-Read-Hall rate of 2.4ϫ10 8 s Ϫ1 and an Auger coefficient of 7ϫ10 Ϫ27 cm 6 /s. In addition, we estimate the carrier capture efficiency into the wells to be ϳ52% and have demonstrated that carrier cooling, cross-well transport, and capture are complete within ϳ10 ps after excitation.

Spin-splitting energies of wurtzite AlN and InN are calculated using the linear combination of atomic orbital method, and the data are analyzed utilizing the two-band k • p model. It is found that in the k • p scheme, a spin-degenerate surface exists in the wurtzite Brillouin zone. Consequently, the D'yakonov-Perel' spin relaxation mechanism can be effectively suppressed for all spin components in the ͓001͔-grown wurtzite quantum wells ͑QWs͒ at a resonant condition through application of appropriate strain or a suitable gate bias. Therefore, wurtzite QWs ͑e.g., InGaN/AlGaN and GaN/ AlGaN͒ are potential structures for spintronic devices such as the resonant spin lifetime transistor.

Auger recombination is studied in InN thin films using an ultrafast time-resolved photoluminescence apparatus. The decay rates are analyzed with nonlinear dependence of the photoluminescence intensity on the carrier concentration. The fitted radiative recombination coefficients at a temperature of 35K are consistent with the theoretical prediction. The Auger rates are small at low carrier concentrations but increase quadratically with the carrier concentration. The Auger activation energies of 4.3 and 9.0meV obtained from the temperature-dependent Auger coefficient indicate that Auger recombination is weakly dependent on temperature and is a phonon-assisted process.