Ultrasmall and ultralow threshold GaInAsP-InP microdisk injection lasers: design, fabrication, lasing characteristics, and spontaneous emission factor

We have calculated lasing characteristics of current injection microdisk lasers of several microns in diameter, taking account of the scattering loss at center posts and the carrier diffusion effect. We found that the optimum width of the disk wing exposed to the air is 0.6-0.7 μm and the minimum threshold current is nearly 10 μA for the disk diameter of 2 μm. The internal differential quantum efficiency can be 95% if the transparent carrier density is reduced to 7.5×10¹⁷ cm^-3 and the diffusion constant is increased to 8 cm²/s. In the experiment, we have obtained the room temperature continuous-wave operation of a GaInAsP-InP device of 3 μm in diameter, for the first time, with a record low threshold of 150 μA. This achievement was mainly owing to the reduction of the scattering loss at the disk edge, and hence the reduction of the threshold current density. The spontaneous emission factor was estimated to be 6×10^-3. This value was much reduced by the large detuning of the lasing wavelength against the spontaneous emission peak. A larger value over 0.1, which is expected for such a small device, will be obtained by the wavelength tuning and the narrowing of the spontaneous emission spectrum