Semiconductor Radiation Research Articles

Spontaneous and Stimulated Recombination Radiation in Semiconductors

Spectral line shapes of the radiation produced by band-to-band recombination of excess carriers in semi-conductors are calculated under the assumption that the momentum matrix element is the same for all initial and final states, i.e., that there is no momentum selection rule. The peak of the stimulated radiation falls at a lower photon energy than does the peak of the spontaneous radiation, except when $T=0$\ifmmode^\circ\else\textdegree\fi{}K. Some numerical results are given for simple parabolic bands, specifically for the case of electron injection into $p$-type GaAs, and are used to deduce the temperature dependence of the forward current which is necessary to maintain a fixed gain in the active region of a diode. The result is closely related to the temperature dependence of the threshold current in an injection laser, and gives reasonable agreement with experiment. The effect of a conduction band tail is briefly considered.

Optical absorption and recombination radiation in semiconductors due to transitions between hydrogen-like acceptor impurity levels and the conduction band

A simplified theory is given of the expected form of the optical absorption and recombination radiation spectra due to direct transitions between hydrogen-like acceptor levels and the conduction band in a semiconductor with simple bands. Some necessary modifications to the simple theory are discussed, and it is shown that transitions from acceptor levels could be the cause of an observed shift of the absorption edge to longer wavelengths on passing from n- to p-type GaAs. For recombination radiation, some experimental curves on the III–V compounds which probably involve transitions to impurity levels are rather broader than those predicted by the simple theory.

On the Theory of Optical Absorption in Metals and Semiconductors

A quantum-mechanical method is described for calculating the effect on the optical absorption of metals and semiconductors of any of the factors responsible for electrical resistance. In this method the electrons which are scattered by imperfections in the crystal lattice are considered to absorb light by a photoelectric process. The calculation is carried out for the case where the conduction electrons are scattered by dissolved impurities. A first order approximation method is used. The results obtained are compared with those of the semi-classical theory used in existing textbooks, in which the current set up by the light is assumed to be damped by the impurities. It is found that the two methods give very similar results for metals. For semiconductors, on the other hand, the approximate method used here gives considerably less absorption than the semi-classical method. The use of exact wave functions for the very slow electrons in semiconductors would give greatly increased absorption coefficients because the intensity of these wave functions is high near the scattering centres. It is suggested that in this way the high absorption of infra-red radiation in semiconductors can be explained.