Al(Ga)InP subwavelength structures (SWS) were fabricated and optimized through thermally dewetted Au nanotemplate and ICP pattern-transfer. When λ< 900 nm, most AlGaInP nanostructures exhibit the reflectivity of less than 2% and insensitive to the incident angle up to 45°. When λ extends to 1800 nm, the reflectivity of less than 5% over 0°-45° is achieved in the optimized nanostructure, which benefits III-V multi-junction solar cells to improve their efficiency. Moreover, not only is such cost-effective nano-fabrication process completely compatible with the other processing of III-V solar cells, but their defined disordered SWS benefit the antireflection performance over broadband and wide view according to the comparison between the measurement and simulation results from AlGaInP SWS.

In this paper, a laterally coupled distributed feedback (LC-DFB) laser based on modulation p-doped multiple InAs/GaAs quantum dot (QD) structures has been fabricated. The device exhibits a high side-mode suppression ratio (SMSR) of > 47 dB and a high thermal stability of dλ/dT = 0.092 nm/K under continuous-wave (CW) operation, which is mainly attributed to the high material gain prepared by modulation p-doping and rapid thermal annealing (RTA) process, and the significantly reduced waveguide losses by shallow-etched gratings and its close proximity to the laser ridge feature in the LC-DFB laser. With this superior performance of the DFB laser, the wide tunable dual-wavelength lasing operation has been obtained by delicately defining different periods for the grating structures on the two sides of the laser ridge or combining the reduced laser cavity length. The wavelength spacing between the two lasing modes can be flexibly tuned in a very wide range from 0.5 to 73.4 nm, corresponding to the frequency difference from 0.10 to 14 THz, which is the largest tuning range by the utilization of single device and hence providing a new opportunity towards the generation of CW THz radiation.

The modulation response of monolithically integrated external optical injection-locking (EOIL) semiconductor ring lasers based on photon-photon resonance effect was systematically analyzed. The simulation results show that the modulation response of the EOIL laser is strongly dependent on the internal loss of the ring laser. Assuming that the waveguide was loss-free, the modulation bandwidth of as high as 67.5 GHz was predicted. However, due to the excessive loss associated with the bending waveguide of the circular-shaped ring laser, the modulation performance of such EOIL laser has no any advantage over its free-running counterpart. Instead, use of rectangular-shaped ring laser as the slave laser is proposed to circumvent the issue associated with the excessive waveguide loss, since the internal loss, in this case, is only dependent on the reflectivity of the total reflection mirrors. Simulation shows the modulation bandwidth of at least 38 GHz is achievable in such EOIL laser, provided the reflectivity of the total reflection mirrors is greater than 96%. It is believed that this theoretical study will facilitate the future experimental demonstration of the monolithically integrated EOIL lasers.

We report on our fabrication and characterization of Al₂O₃/Si composite nanodome (CND) structures, which is composed of Si nanodome structures with a conformal cladding Al₂O₃ layer to evaluate its optical and electrical performance when it is applied to thin film solar cells. It has been observed that by application of Al₂O₃thin film coating using atomic layer deposition (ALD) to the Si nanodome structures, both optical and electrical performances are greatly improved. The reflectivity of less than 3% over the wavelength range of from 200 nm to 2000 nm at an incident angle from 0° to 45° is achieved when the Al₂O₃ film is 90 nm thick. The ultimate efficiency of around 27% is obtained on the CND textured 2 μm-thick Si solar cells, which is compared to the efficiency of around 25.75% and 15% for the 2 μm-thick Si nanodome surface-decorated and planar samples respectively. Electrical characterization was made by using CND-decorated MOS devices to measure device’s leakage current and capacitance dispersion. It is found the electrical performance is sensitive to the thickness of the Al₂O₃ film, and the performance is remarkably improved when the dielectric layer thickness is 90 nm thick. The leakage current, which is less than 4x10⁻⁹ A/cm² over voltage range of from -3 V to 3 V, is reduced by several orders of magnitude. C-V measurements also shows as small as 0.3% of variation in the capacitance over the frequency range from 10 kHz to 500 kHz, which is a strong indication of surface states being fully passivated. TEM examination of CND-decorated samples also reveals the occurrence of SiO_x layer formed between the interface of Si and the Al₂O₃ film, which is thin enough that ensures the presence of field-effect passivation, From our theoretical and experimental study, we believe Al₂O₃ coated CND structures is a truly viable approach to achieving higher device efficiency.

Loss-reduction in flexibly vertical coupled ring lasers is demonstrated through asymmetric double shallow ridge in the main ring area and inductively coupled plasma (ICP)/ICP cascade etching. Compared with the previous counterpart, the reduced threshold current and enhanced output power are obtained; coupling ratio is tuned from 27% to 1.5% when threshold current is varied from 60 to 80 mA. Single-mode lasing with sidemode-suppression ratio of 27 dB and quality factor of 13120 is achieved when I _c=15 mA, I _d=58 mA, which are nearly twofolds of that in the previous one. Such strategies can be widely employed to reduce loss in other vertical coupled photonic circuits.