Figure 1.

(a, b) show schematics of devices used for the present study. (a) shows the standard, referential, VCSELs with a curved mirror on one side. (b) shows the VCSEL with a cylindrical lens investigated in the present study. The distance between the top and bottom mirrors is 20–30 µm. The thickness of p-GaN is approximately 100 nm. InGaN multi quantum-well (MQW) is approximately 20 nm including the barrier layers. Thus, the rest of cavity is occupied by n-GaN. Top and bottom side Distributed Bragg reflector (DBR) are designed to have reflectivity of 99.7% and > 99.9%, respectively. Those devices are fabricated over (0001) plane of GaN substrate. The x-, y-, and z-directions of the GaN substrate are $〈1-100〉,〈11-20〉,\text{and}〈0001〉$, respectively. The fabricated devices have the structure shown in (b). Thus, a cleaved facet was introduced along the dashed line. (c, d) are the images of device shown in (b) with and without facet. Additional mechanical damage was introduced in the facet shown in (d) by the hitting a probe for measurement. These are recorded under pulsed current injection above the threshold current (RT, 1 µs, 0.1%, 17.7 k/cm²). (e) show schematics of conventional semiconductor lasers, edge emitting lasers, VCSELs, PCSELs and the present one.