Characteristics of GaAs lasers near room temperature

The efficiency and threshold of GaAs lasers can be affected by a delay occurring between the application of a current pulse and the laser output. The delays may be some tenths of a microsecond in certain diffused junction lasers when operated near room temperature, e.g., when the donor substrate dopant is selenium with a concentration of the order of 10¹⁸atoms per cm³. No such delays are observed in diodes in which the substrate dopant is silicon. In the case of selenium, the delay depends on the doping level, decreasing as the concentration increases. The delay is also very sensitive to injection current, decreasing rapidly with increasing current from its maximum at threshold. During the pulse, after lasing commences, the output continues to increase. A similar effect has also been observed with spontaneous emission. Operation of these devices below room temperature shows that the delay is also dependent on temperature. The delay decreases over a fairly narrow temperature range and in all cases is no longer observed ( < 20 n/s) below -70°C. These observations are explained by considering the effect of impurity trapping levels which may be associated with the