A high-power 7xx-nm semiconductor laser is the core pump source of thulium-doped fiber, alkali metal gas, and metal vapor lasers and has important applications. Compared with 9xx-nm-band near-infrared (NIR) semiconductor lasers, 7xx-nm-band devices usually have waveguide layers and claddings with high aluminum components to maintain good carrier limitation because of their high photon energy; low material mobility leads to increased device resistance and lower carrier injection efficiency. However, high-aluminum component materials easily form oxygen defects during epitaxial growth and cavity surface cleavage, resulting in a low catastrophic light damage threshold power. Therefore, simultaneously achieving high power and high efficiency with 7xx-nm semiconductor lasers is highly challenging.

A laser epitaxial sheet is grown on an N-type highly doped GaAs substrate via metal-organic compound vapor deposition (MOCVD). The fabrication process of the device is similar to that of traditional lasers. First, a 200-μm-wide mesa is formed via photolithography and wet etching. A 200-nm-thick SiO₂ electrical insulation layer is grown using plasma-enhanced chemical vapor deposition (PECVD) equipment. A 190-μm-wide current injection window is prepared using the reactive ion beam (RIE) dry method combined with wet etching. A Ti/Pt/Au metal electrode is deposited on the P plane and alloyed. The laser-wafer substrate is thinned and polished, after which the AuGeNi/Au metal electrode is deposited onto the N surface and alloyed via rapid thermal annealing. After the wafer preparation is completed, the wafer is cleaved into a 4-mm cavity length bar by a splitter under the atmospheric environment, and then the cavity surface is passivated and coated. To improve the catastrophic optical mirror damage (COMD) level of the cavity surface, the ZnSe film is deposited after cleaning and passivation, and then the anti-reflection film with a reflectance of 2.8% and the high-reflectance film with a reflectance of 98% are evaporated on the front and back cavity surfaces, respectively. Finally, the bar is cut into a single-tube chip, and the chip is welded onto the AlN heat sink with the P-side down using a chip mounter. The performance of the device is tested. The device is tested at various temperatures using thermoelectric cooler (TEC).

Figure 2 shows the power?current?voltage (L-I-V) characteristics of the laser measured at the 25 ℃ heat sink temperature and continuous operation conditions. The threshold current of the laser is 1.24 A, and the corresponding threshold current density is 155 A/cm². The slope efficiency of the laser is 1.33 W/A, the series resistance is 15.5 mΩ, and the continuous power is 13 W at a current of 11 A; the corresponding power conversion efficiency is 66%, and the maximum photoelectric conversion efficiency is 66.6%. Figure 3(a) shows the far-field distribution measured by the laser under a continuous current at room temperature and 10 A. The vertical divergence angle is 32.2°, and the vertical far-field divergence angle of the beam with 95% power ratio is 49.8°. The full width at half-maximum of lateral far-field divergence angle and lateral far-field divergence angle (B) of the beam with 95% power ratio are 6.3° and 7.4°, respectively. Figure 3(b) shows the laser lasing spectrum measured at room temperature and a current of 10 A, with a visible peak wavelength of 780.83 nm and a full width at half-maximum of spectrum of 1.77 nm. The L-I-V characteristics of the device under quasi-continuous operation conditions (pulse width of 100 μs) are also tested, as shown in Fig. 4. The peak power of the device at a current of 12.7 A is 16.3 W, the corresponding conversion efficiency is 69%, and the maximum power conversion efficiency is 70% (when the output power is 14.3 W). Figure 5 shows the lateral far-field distribution and lateral divergence angle with respect to temperature. When the heat sink temperature increases from 15 ℃ to 60 ℃, the change in B is almost 0. At 30 ℃, the lateral far-field development exhibits large broadening. The lateral far-field distribution of the laser at 25 ℃ and under different currents is shown in Fig. 6. As the current increases, the lateral far field of the laser gradually widens. At a current of 2.0 A, B is 5.2°, and when the current is increased by 9.0 A, B increases to 7.2°. The output characteristics of the laser are measured in the temperature range of 5?60 ℃, and the operation current is continuous at 5 A. The changes in the threshold current and slope efficiency of the laser with respect to temperature are shown in Fig. 7. The two intervals of 15?30 ℃ and 35?60 ℃ are selected to calculate the characteristic temperature, and T0 and T1 obtained in these two intervals are as follows: T0 is 210.97 K and T1 is 434.78 K, and T0 is 139.86 K and T1 is 418.41 K, respectively. Using the data on ΔT and ΔPdis obtained from the input current and lash-wavelength in Fig. 8, Fig. 9 is obtained by tracing point fitting, and the thermal impedance Rth of the device is (3.57±0.13)℃/W according to the slope of the fitting curve.

In this study, a high-power semiconductor laser with an operation wavelength of 780 nm is developed. Using a GaAsP quantum well to increase the barrier height and suppress carrier leakage, a high-efficiency epitaxial structure with low internal loss is obtained in combination with the design of an asymmetric large optical cavity. The prepared 200-μm stripe laser achieves a quasi-continuous output power of 16.3 W and a continuous output power of 13 W, and the corresponding photoelectric conversion efficiency reaches 69% and 66%, respectively. The lateral far field of the laser does not change significantly with temperature but widens significantly with an increase in the working current. By testing the threshold current and slope efficiency of the device at different temperatures, the characteristic temperatures T0 and T1 are found to be 210.97 K and 434.78 K, respectively, in the range 15?30 ℃, and 139.86 K and 418.41 K, respectively, in the range 35?60 ℃. The measured thermal resistance of the laser is 3.57 ℃/W, which is relatively large, indicating that the heat dissipation effect of the device is poor, and the next step must be to improve the device preparation and packaging technology to further improve the conversion efficiency.