K.L. Shaklee

DIRECT DETERMINATION OF OPTICAL GAIN IN SEMICONDUCTOR CRYSTALS

We report a new technique for measuring the stimulated emission spectrum and optical gain of semiconductor materials. Amplified spontaneous emission is used to determine the gain factor by relating the measured variation in light output to variation in the length of the excitation beam. Results for CdS crystals at 2°K are presented that indicate net gains as high as 160 cm−1 at λ = 4907 A are possible with ∼ 12‐MW/cm2 optical pump power density from a nitrogen laser.

Optical gain in semiconductors

Abstract Direct measurements of optical gain in semiconductors give information on the stimulated recombination process that cannot be easily obtained from an oscillating semiconductor laser. The effects of various material parameters on the gain and saturation factors can be easily studied. The temperature dependence of the stimulated recombination in high purity GaAs will be presented as an example. The pertinence of the gain and saturation factors to the threshold and efficiency of semiconductors laser oscillators will be discussed. The significance of gain measurements on GaP doped with isoelectronic traps will be considered in terms of the observed gain and saturation properties.

Stimulated Emission and Laser Action in Gallium Nitride

Stimulated emission and laser action have been observed near 3.45 eV in single‐crystal needles of GaN. These observations support the earlier suggestion that GaN is a direct band‐gap semiconductor with Eg∼3.50 eV at 2°K. Furthermore, the occurrence of very high gain (g∼105 cm−1) in the stimulated emission emphasizes the possible device potential of this material.

Optical Gain in Lightly Doped GaAs

Measurements of both small‐signal gain and stimulated emission spectra for optically pumped GaAs are described. Saturation of the amplification process is shown to play an important role in determining the spectral distribution of the stimulated emission. These measurements indicate that intrinsic gain in high‐purity material does not result from band‐to‐band recombination and in its place an interpretation in terms of free‐exciton radiative Auger recombination is suggested.

Stimulated emission and the type of bandgap in GaSe

Abstract Stimulated emission has been observed in single crystal ϵ-GaSe. Considerations of the spontaneous emission spectrum and the threshold for stimulated transitions are used to show that previous reports that this material has an indirect gap are incorrect. At 2°K the stimulated emission peaks at 6010 A, which is ≈ 45 meV below the direct exciton absorption peak at 5800 A.

A NEW MODEL FOR THE TEMPERATURE‐DEPENDENT CdS LASER

The temperature dependence of laser wavelength and threshold pump power of a CdS platelet laser operating from 2 to 240°K are presented. A model is proposed that demonstrates how the temperature dependence of band edge absorption determines the variation of laser wavelength and threshold pump power over this temperature range.

Considerations relevant to Bose condensation of excitonic molecules in CdSe

Abstract The transition temperature for an anisotropic Bose gas, and the lattice temperature rise following pulsed photo-excitation, are computed. Comparison with experimentally realizable conditions shows that Bose condensation of excitonic molecules in CdSe cannot be attained following pulsed photoexcitation.

Magnetoluminescence studies of excitonic scattering processes in high purity GaAs

Abstract The broad emission line at about 1.512 eV, which dominates the emission spectra of pure GaAs at intermediate excitation levels (1–300 kW/cm2) and low temperatures (

Quantum effects in the magnetoluminescence of the electron-hole plasma in GaAs

Abstract Magnetoluminescence studies of GaAs at high excitation levels show that the degeneracy of the electron-hole plasma decreases gradually with increasing magnetic field. Theoretical analysis of the data shows that taking into account quantum effects of free carriers is sufficient to describe the magnetic field behavior of the plasma.