INJECTION LASER STUDY.
Rept. no. 8, 1 Jun 63-31 May 65 (Final),
THOMAS J WATSON RESEARCH CENTER YORKTOWN HEIGHTS N Y
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Many GaAs injection laser diodes show a substantial delay between the application of a current pulse and the onset of lasing if they are operated near room temperature and at currents just above threshold. A model for this effect based on trapping of carriers gives good agreement both with the delay results and with experimental data on the time dependence of spontaneous emission for currents below threshold, provided that the density of trapping states is about ten times the threshold carrier concentration. No independent evidence for the existence of these states has been obtained. The dependence of current and light emission on voltage in CdTe diodes was studied. The current varies as expqV2kT at low current levels, and as exp qVkT at higher current levels. Emission is observed with photon energies considerably greater than the applied voltage. Thermodynamic considerations restrict the efficiency of such radiation from one-step processes, and account in part for the low quantum efficiency found at room temperature. In GaAs structures with a high-resistance p-type layer surrounded by high-conductivity p-type layers, ambipolar negative resistance, efficient light emission, and lasing were observed. The origin of the electrons is thought to be avalanching in the strong electric field found to present in these all p-type structures.
- Lasers and Masers
- Solid State Physics