The absorption coefficient for a 0.4-μm-thick GaN layer grown on a polished sapphire substrate was determined from transmission measurements at room temperature. A strong, well defined exciton peak for the A and B excitons was obtained. The A, B, and C excitonic features are clearly defined at 77 K. At room temperature, an energy gap Eg=3.452±0.001 eV and an exciton binding energy ExA,B=20.4±0.5 meV for the A and B excitons and ExC=23.5±0.5 meV for the C exciton were determined by analysis of the absorption coefficient. From this measured absorption coefficient, together with the detailed balance approach of van Roosbroek and Shockley, the radiative constant B=1.1×10−8 cm3/s was obtained.

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The absorption coefficient α for GaAs at room temperature was determined in the spectral range from 1.3 to 1.6 eV by transmission measurements for 10⩽α⩽103 cm−1 and by a Kramers−Kronig analysis of the reflectance for α≳103 cm−1. Measurements were made on high−purity n−type samples, n−type samples with free−electron concentrations from 5×1016 to 6.7×1018 cm−3, p−type samples with free−hole concentrations from 1.5×1016 to 1.6×1019 cm−3, and p−type samples heavily doped with the amphoteric impurity Si. These data show that near the direct energy gap Eg the shape of the α−vs−photon−energy curve is strongly dependent on the impurity concentration.

Measurement of the room temperature forward bias current-voltage behavior of InGaN/AlGaN double heterostructure blue light-emitting diodes demonstrates a significant departure from the usual Is exp(qV/ nkT) behavior where n is the ideality factor which varies between 1 and 2. The observed current-voltage behavior at room temperature may be represented as I=2.7×10−11 exp(5.7V) which suggests a tunneling mechanism. Measurement of the electroluminescence for currents from 0.5 to 100 mA demonstrates that the emission peak shifts to higher energy while increasing in intensity. The shifting peak spectra is due to band filling, a process which results from the injection of holes via tunneling into an empty acceptor impurity band and vacant valence band tails. At currents near 100 mA, a non-shifting band-to-band emission approaches the intensity of the shifting peak spectra. The active layer of these diodes is codoped with both the donor Si and the acceptor Zn.

A model for the calculation of the absorption and emission spectra for GaAs at carrier concentrations in excess of 1×1018 cm−3 is described. This model utilizes a Gaussian fit to Halperin-Lax band tails for the concentration-dependent density of states and also includes an energy-dependent matrix element. The calculated absorption and emission spectra are compared to previous experimental results. All results are for 297 K. For p-type GaAs, the agreement is very good. The concentration dependence of the effective energy gap is obtained and can be expressed as Eg (eV) =1.424−1.6×10−8 [p (cm−3)]1/3. The concentration-dependent thermal equilibrium electron-hole density product n0p0 and the radiative lifetime τr are calculated for p-type GaAs. The value of n0p0 increases from the low-concentration value of 3.2×1012 cm−6 to 1.2×1013 cm−6 at p=1.6×1019 cm−3. This value of n0p0, together with the thermal generation rate obtained from the experimental absorption coefficient, gives τr as 0.37 nsec at p=1.6×1019 cm−3.