Single-heterostructure distributed-feedback GaAs-diode lasers

This paper reports the fabrication, testing, and analysis of distributed-feedback (DFB) single-heterostructure (SH) electrically pumped GaAs lasers. The techniques of fabricating the DFB grating and diode using interferometric exposure of photoresist, development, ion milling, liquid-phase-epitaxial growth, and diffusion are described in detail. Next, experimental results on a variety of diodes operating at 77 K are presented. It is shown that narrow laser linewidth (< 0.15 Å) and low threshold operation (775 A/cm²) can be obtained. Also reported is output coupling from the grating which results in highly collimated laser beams with divergence of approximately 0.35°. Coupling coefficients, which determine laser threshold, are computed as a function of device parameters including physical dimensions, refractive indices, grating size and shape, and Bragg order for single-and double-heterostructure geometries. Calculated and measured thresholds are shown to be in good agreement.