High-Pulsed-Power (49W) Vertical-Cavity Surface-Emitting Laser with Five Quantum Wells by Uniform Current Injection into Large Emitting Area

−47− Vertical-cavity surface-emitting lasers (VCSELs) are attractive for various applications because of their low cost, ease of designing two-dimensional arrays, and the low divergence angles of the output beam, provided that the issue of their relatively low output power is addressed. The maximum output power of previously reported VCSELs was just over 2 W for CW operation and just over 20 W for pulsed operation, both of which were achieved by driving arrayed VCSELs in parallel 2) 3). However, a multiple light source array structure is not suitable for applications such as light detection and ranging (LIDAR) as it complicates the optical system for emitting and detecting light in various directions. Therefore a single emitter VCSEL with an output power of over 10 W, which is the typical output power of LIDAR, is needed. The output power of a single emitter VCSEL is limited by thermal rollover caused by Joule heat, so a high power single emitter VCSEL needs to have a low thermal resistance with a large active diameter over 100μm and a bottom-emitting structure 4)-6). Previously, we reported the maximum output power of 12.5W was achieved by a single VCSEL with five quantum well under a pulsed operation with a pulse width of 50ns and a repetition rate of 1kHz 7). In a large bottom-emitting VCSEL, the active region is close to the p-type electrode and separate from the n-type electrode located on the outside of the emitting area. This causes the non-uniformity of current injection into the active region 8). Previously we reported that the non-uniformity of current injection was caused by the band discontinuity at the interface between AlAs and GaAs of the n-type Distributed Bragg Reflector (DBR) 1). The purposes of this study were to achieve high peak pulsed output power from a single VCSEL device under a short-pulsed operation with a pulse width of 10ns by suppression of the non-uniformity of current injection and the carrier overflow in active region. A schematic device structure of our VCSEL, which was produced by metal-organic vapor-phase epitaxy, is shown in Fig. 1. The VCSEL structure consists of the active region sandwiched between 21-period n-type DBR and 25-period p-type DBR. The active region, which contains 6nm-thick In0.2Ga0.8As multiple quantum wells (QWs) separated by 8nm-thick GaAs barriers, is surrounded by AlGaAs cladding layers to form a one wavelength cavity. Both types of DBR consist of alternating the quarter-wavelength layers …