Infrared photoluminescence (PL) from InSb, InAs, and InAs1−xSbx (x<0.3) epitaxial layers grown by atmospheric pressure organometallic vapor phase epitaxy has been investigated for the first time over an extended temperature range. The values of full width at half maximum of the PL peaks show that the epitaxial layer quality is comparable to that grown by molecular‐beam epitaxy. The observed small peak shift with temperature for most InAs1−xSbx epilayers may be explained by wave‐vector‐nonconserving transitions involved in the PL emission. For comparison, PL spectra from InSb/InSb and InAs/InAs show that the wave‐vector‐conserving mechanism is responsible for the PL emission. The temperature dependence of the energy band gaps, Eg, in InSb and InAs is shown to follow Varshni’s equation Eg(T)=Eg0−αT2/ (T+β). The empirical constants are calculated to be Eg0=235 meV, α=0.270 meV/K, and β=106 K for InSb and Eg0=415 meV, α=0.276 meV/K, and β=83 K for InAs.

Photoluminescence of InSb, InAs, and InAsSb grown by organometallic vapor phase epitaxy.

Light-emitting diodes (LEDs) are devices designed to efficiently convert electrical energy into electromagnetic radiation, most of which is visible to the human eye. Some of the disciplines involved in the understanding and utilization of LEDs are reviewed, with emphasis on the III-V semiconducting compounds and GaP LEDs in particular. Salient features of photometry, the physics of electrical injection and luminescence, and the design of LEDs are discussed in detail, followed by a survey of prominent applications for the various LEDs.

Light-emitting diodes

It has become well established during the last few years that intense photoexcitation of a semiconductor leads to the heating of the carriers and the generation of nonequilibrium phonons. These phenomena which result from the relaxation of photoexcited carriers to the band extrema by interaction with other carriers and by emission of phonons, are reviewed in this paper. At relatively low intensities ( 5 W/cm 2 for GaAs) the photoexcited carrier distribution is Maxwellian with a carrier temperature T e different from the lattice temperature. T e as high as 150K and effective phonon temperatures as high as 3700K have been observed in GaAs. The observed variation of T e with excitation intensity leads to the conclusion that in semiconductors like GaAs the polar optical mode scattering is the dominant energy loss mechanism from the electron gas to the lattice. Similar results are obtained in CdSe and CdS. At higher intensities (>10 5 W/cm 2 for GaAs), the carrier dist0ribution becomes non-Maxwellian for reasons not well understood at present. We will also discuss some recent measurements of variation of T e with excitation wavelength and of the transmission spectra of photoexcited GaAs.

Hot electrons and phonons under high intensity photoexcitation of semiconductors

An analysis is made of the theory of the luminescence spectra of semiconductors with direct optical transitions involving recombination of nonequilbrium carriers whose energies are close to the band gap edges. The usual formulation of the theory of recombination is employed, i.e., given densities of free electrons and holes are assumed. The first part of the review is concerned with the luminescence (of the exciton, interband, impurity, or interimpurity type) of lightly doped semiconductors. Unsolved problems are noted and it is stressed particularly that the interband luminescence spectrum is governed largely by the interaction of carriers and by the mechanisms of their scattering, but in practice this has been ignored so far in the development of the theory and in the interpretation of the experimental results. The second (main) part of the review is devoted to the luminescence of heavily doped semiconductors. It is shown that the nature of the electron spectrum of such semiconductors, involving formation of density-of-states "tails" and broadening of the impurity levels, is manifested clearly in this case. It is stressed that the distribution of nonequilibrium carriers between localized states corresponding to a continuous spectrum is usually quite different from the quasiequilibrium distribution, i.e., it cannot be described by introduction of the quasi-Fermi level. An allowance for this circumstance makes it possible to explain a great variety of seemingly contradictory experimental data on the luminescence spectra of heavily doped semiconductors. The deviation of the carrier distribution from the quasiequilibrium case is manifested also in transient characteristics of the luminescence, and it also governs the characteristic features of radiative recombination in strongly compensated heavily doped semiconductors, which can be regarded as one of the models of amorphous semiconductors. It is pointed out in conclusion that the proposed concepts can account for the special features of the characteristics of electroluminescent structures made of heavily doped semiconductors.

http://iopscience.iop.org/article/10.1070/PU1981v024n03ABEH004770/pdf

Edge luminescence of direct-gap semiconductors

Inter-impurity recombinations in semiconductors

Optically excited recombination emission has been studied for $n$- and $p$-type single-crystal samples of InSb at 77 and 4.2\ifmmode^\circ\else\textdegree\fi{}K. Emissions associated with band-to-band transitions, transitions with creation of an optical phonon, and transitions involving acceptor impurities have been observed. The band-to-band emission in the pure samples can be attributed to direct transitions, whereas the emission in samples of high donor concentrations clearly shows transitions violating wave-vector conservation. The emission of phonon-assisted transitions is about 150 times weaker than that of direct transitions; this ratio is consistent with the strength of polar-mode coupling. The $n$-type as well as the $p$-type samples show an emission band due to electron transitions from the conduction band to some impurity level at 7.5 meV above the valence band, and the emission is much more prominent in the Zn-doped samples. Germanium-doped $p$-type samples show a weak emission band associated with an acceptor level at 17 meV above the valence band. Samples of large donor concentrations show the effect of band tailing. The main impurity emission increases linearly while the band-to-band emission increased quadratically with the intensity of exciting light. From the shift and splitting of the emission under applied magnetic field, an electron effective mass of ${m}_{e}\ensuremath{\sim}0.018m$ and an electron $g$ factor of $|g|=40 \mathrm{at} 30$ kG are obtained. Electroluminescence has been observed in $p$-type crystals under pulsed electric fields of \ensuremath{\sim}60 V/cm. The observed spectrum appears to be a broadened impurity line. The emission is more than an order of magnitude weaker than optically excited emission corresponding to the same sample conductance.

Aram Mooradian

Papers

Recombination Emission in InSb