A high slope efficiency vertical-cavity surface-emitting laser (VCSEL) is described. The InGaAs/GaAsP strain compensated multiple quantum wells (MQWs) are designed by PICS3D. The wavelength redshift occurs due to the thermal effect, the lasing wavelength of MQWs is designed to be around 928 nm. The active region consists of five compressively strained 4.4 nm thick In_0.16Ga_0.84As quantum wells separated and surrounded by 6.2 nm thick GaAs_0.88P_0.12 tensile strained compensation layers to obtain the high quantum efficiency and ensure the stress release. Subsequently, the MQWs are grown by metal-organic chemical vapor deposition (MOCVD) and the photoluminescence (PL) spectrum is measured using an Nd:YAG laser (532 nm excitation), of which the peak wavelength is approximately 928 nm and the full width at half maximum is nearly 17.1 nm. The resonant cavity is surrounded by p- and n-DBRs. The n-DBRs are designed to be a 28-period AlAs/Al_0.12Ga_0.88As and 3.5-period Al_0.90Ga_0.10As/Al_0.12Ga_0.88As, and the p-DBR is designed to be a 23-period Al_0.90Ga_0.10As/Al_0.12Ga_0.88As. The thickness of each a material is <inline-formula><tex-math id="M2">\begin{document}$\lambda/4n$\end{document}</tex-math><alternatives><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="6-20181822_M2.jpg"/><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="6-20181822_M2.png"/></alternatives></inline-formula> (<inline-formula><tex-math id="M3">\begin{document}$\lambda$\end{document}</tex-math><alternatives><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="6-20181822_M3.jpg"/><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="6-20181822_M3.png"/></alternatives></inline-formula> = 940 nm, <i>n</i> represents refractive index), and 20 nm graded layer is inserted in the interface between two types of materials. The p-/n-DBRs’ experiment PL reflection spectra (using a white illuminant) are carried out, the central wavelength is around 938.7 nm, and the reflectivity values of p-/n-DBRs are nearly 99.0% and 99.7%, respectively. The VCSELs are grown by MOCVD technique, and treated by dry etching, wet oxidation, metal electrode technology and other processes. In the process of dry etching, the top mesa is treated by inductively coupled plasma with BCl₃ and Cl₂ chemistry. In order to expose the oxide layer the wet oxidized process is carried out, and the etching depth is nearly 3500 nm. An oxidation furnace is heated for 15 min prior to oxidation. Then the oxide aperture is shaped by the wet nitrogen oxidation furnace at 425 °C with an N₂ flow of 200 sccm, and the oxide rate is approximately 0.40 <inline-formula><tex-math id="M4">\begin{document}${\text{μm}}$\end{document}</tex-math><alternatives><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="6-20181822_M4.jpg"/><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="6-20181822_M4.png"/></alternatives></inline-formula>/min for A_0.98Ga_0.02As. The diameter of oxide aperture is made into an 8 <inline-formula><tex-math id="M5">\begin{document}${\text{μm}}$\end{document}</tex-math><alternatives><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="6-20181822_M5.jpg"/><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="6-20181822_M5.png"/></alternatives></inline-formula> diameter. In the process of metal electrode technology, AuGeNi alloy is sputtered on the top surface to form p-type ohmic contact, and Ti/Pt/Au is evaporated on the back surface of substrate to form an n-type ohmic contact. Rapid thermal annealing at 350 °C in a nitrogen atmosphere is carried out subsequently to obtain a good-quality ohmic contact. Finally, we test the VCSELs’ <i>L-I-V</i> characteristics and spectra in different areas. In area 1, room-temperature lasing at around 940 nm is achieved with a threshold current of 0.95 mA, a slope efficiency of 0.96 W/A, and an output power of 4.75 mW. In area 2, threshold current is 1 mA, a slope efficiency is 0.81 W/A at 25 °C and threshold current is 1.9 mA, slope efficiency is 0.57 W/A at 25 °C. The output power values reach up to 3.850 mW and 2.323 mW at 25 °C and 80 °C, respectively.

At present, solar cells are the main sources for spacecrafts. For a long time the bulk of the space power installations has been the solar arrays based on single junction silicon and gallium arsenide solar cells. In recent years a trend has been the active use of triple-junction GaAs solar cell with higher efficiency instead of single junction solar cells. One of the most important characteristics of solar cells used in spacecrafts is the resistance to radiation damages caused by high energy particles of the near-Earth space. According to the spectral response of triple-junction GaAs solar cell and the damage characteristics of the current under the condition of electron irradiation, the physical mechanism of cell attenuation can be determined: the current degradation originates mainly from the GaInAs subcells. These damages form additional centers of nonradiative recombination, which results in the reduction of the minority charge carrier diffusion lengths and in degradation of the solar cells photocurrent.The radiation damage caused by the electron irradiation will shorten the diffusion length of the base region and affect the collection of photo generated carriers. The ways of improving absorption of long wavelength light in GaInAs subcells with a thin base in using the distributed Bragg reflector can be investigated by the mathematical simulation method based on calculating the light propagation in a multilayer structure by means of the TFCalc software which can design optical structure. To estimate the validity of these methods for solar cells structures with distributed Bragg reflector, the spectral dependences of the photoresponse and the reflection coefficient with different base thickness values are calculated and compared with experimental results. Based on the physical mechanism of the degradation, the thickness of middle subcell base layer is reduced, and an appropriate structure of the distributed Bragg reflector is simulated by the TFCalc software. As a result, the new structure solar cells are that the thickness of the base layer is 1.5 m compared with the different middle subcell thickness values, and the distributed Bragg reflector structure with 15 paris of the Al0.1Ga0.9As/Al0.9Ga0.1As with 850 nm central wavelength is embedded in the middle subcell of the base layer, the distributed Bragg reflector has a highest reflectivity of more than 97% in the actual test, and a bandwidth of 94 nm, which can satisfy design requirement. After irradiating the new structure of solar cells, the decay of its short-circuited current is reduced by 50% compared with that of the original structure, and the remaining efficiency factor is increased by 2.3%.

Using transfer matrix method and TFcalc thin film design software,the reflectance spectrum of distributed Bragg reflector (DBR) and vertical cavity surface emitting laser (VCSEL) are simulated.The reflectance spectra from the cavity and surface are compared with each other,thus providing the basis for white light source (WLS) optical reflectance spectrum of the VCSEL epitaxial wafer.When using WLS to characterize VCSEL wafer,it is necessary to combine the simulation results and the shape of optical reflectance spectrum to speculate the reflectance seen from the cavity.The influences of different cap layers on the reflectance of DBRs are discussed theoretically and experimentally.With a 1/4 GaAs cap layer,the reflectance reaches up to 97.8% seen from the cavity.This design can make the wavelength of the VCSEL etalon picked easily because of avoiding the influence of test noise. The active region has higher heat accumulation due to the small area and poor thermal conductivity.The characteristics of the gain spectrum of InGaAs/AlGaAs strained quantum well (QW) under different temperatures and the temperature distribution in VCSEL are simulated by Crosslight software.The gain-to-cavity wavelength detuning is used to improve the slope efficiency and the temperature stability.The temperature in active region ranges from 360 K to 370 K.The gain peak wavelength and the Fabry-Perot cavity wavelength are designed in the ranges of 829-832 nm and 845-847 nm,respectively.Epitaxial wafer with top-emitting VCSEL structure grown by metal-organic chemical vapor deposition is characterized.The room temperature photoluminescence peak is at 827.5 nm and the etalon cavity wavelength measured by optical reflectance is 847.7 nm,which are consistent with designed values. The oxide restricted VCSELs with 7.5 m oxide aperture are fabricated.The image of the infrared light source CCD shows that the oxide aperture is circular.A passivation layer of 120 nm SiO2 is finally deposited to insulate water vapor.The threshold current is 0.8 mA,and the maximum output power reaches up to 9 mW at 13.5 mA.The optical spectrum at 6.0 mA reveals multiple transverse modes.The center wavelength is 852.3 nm and the root mean square (RMS) spectrum width is 0.6 nm,meeting the high-speed Datacom standards.Shannon theory indicates that the maximum data rate is not only proportional to bandwidth but also related to signal-to-noise ratio (SNR).It is effective to reduce relative intensity noise and enhance the SNR by increasing output power.From the eye diagram of 25 Gbit/s on-off key VCSEL,it is demonstrated that fall time is 38.66 ps,rise time is 41.54 ps,SNR is 5.6,and jitter RMS is 1.57 ps.Clear eye opening is observed from eye diagram of 25 GBaud/s PAM-4 VCSEL,which indicates the qualified 50 Gbit/s high speed performance.