Charge carrier scattering channels in graphite bridging its valence and conduction band offer an efficient Auger recombination dynamic to promote low energy charge carriers to higher energy states. It is of importance to answer the question whether a large number of charge carriers can be promoted to higher energy states to enhance the quantum efficiency of photodetectors. Here, we present an experimental demonstration of an effective Auger recombination process in the photo-excited nano-graphite film. The time-resolved hot carrier thermalization was analyzed based on the energy dissipation via the Auger scattering channels. We split the Auger recombination occurrence centered at 0.40 eV energy state into scattering and recombination parts, for characterizing the scattering rate in the conduction band and the recombination rate toward the valence band. The scattering time with respect to the energy state was extracted as 8 ps · eV⁻¹, while the recombination time with respect to the energy state was extracted as 24 ps · eV⁻¹. Our study indicates a 300 fs delay between the hot carrier recombination and generation, leading to a 10⁵ ps⁻¹ · cm⁻³ Auger scattering efficiency. The observed duration for the Auger recombination to generate hot carriers is prolonged for 1 ps, due to the hot carriers energy relaxation bottleneck with optical-phonons in the nano-graphite. The presented analytic expression gives valuable insights into the Auger recombination dynamic to estimate its most efficient energy regime for mid-infrared photodetection.

Direct epitaxial growth of group III-V light sources with excellently thermal performance on silicon photonics chips promises low-cost, low-power-consumption, high-performance photonic integrated circuits. Here, we report on the achievement of ultra-high thermal stability 1.3 µm InAs/GaAs quantum dot (QD) lasers directly grown on an on-axis Si (001) with a record-high continuous-wave (CW) operating temperature of 150 °C. A GaAs buffer layer with a low threading dislocation density (TDD) of 4.3 × 10⁶cm^-2 was first deposited using an optimized three-step growth method by molecular beam epitaxy. Then, an eight-layer QD laser structure with p-type modulation doping to enhance the temperature stability of the device was subsequently grown on the low TDD Si-based GaAs buffer layer. It is shown that the QD laser exhibits the ultra-high temperature stability with a characteristic temperature T₀=∞ and T₁=∞ in the wide temperature range of 10-75 °C and 10-140 °C, respectively. Moreover, a maximum CW operating temperature of up to 150 °C and a pulsed operating temperature of up to 160 °C are achieved for the QD laser. In addition, the QD laser shows a high CW saturation power of 50 mW at 85 °C and 19 mW at 125 °C, respectively.

We report on the significantly improved linewidth enhancement factor (α_H-factor) of 1.3-µm InAs/GaAs quantum dot (QD) lasers by direct Si doping, compared with ones having identical structures but without the Si doping. It is found that the α_H-factors for the ground-state and first excited-state at their gain peak positions of the Si-doped QD lasers are 1.48 and 0.63 while those of the undoped QD lasers are 2.07 and 1.07, greatly decreasing by about 28.5% and 41.1%, respectively. Furthermore, theoretical calculation and analysis suggest that direct Si doping would increase the electron quasi-Fermi level in conduction, leading to the increase in population inversion. Meanwhile, the appearance of a built-in electric field caused by the Si doping would accelerate the capture of electrons into QDs and strengthen the confinement effect of electrons, resulting in an increased differential gain.

We report the significantly enhanced performance of InAs/GaAs quantum dot (QD) lasers on Si(001) by spatially separated co-doping, including n-doping in the QDs and p-doping in the barrier layers simultaneously. The QD lasers are a ridge waveguide of 6 × 1000 µm² containing five InAs QD layers. Compared with p-doped alone laser, the co-doped laser exhibits a large reduction in threshold current of 30.3% and an increase in maximum output power of 25.5% at room temperature. In the range of 15°C-115°C (under 1% pulse mode), the co-doped laser shows better temperature stability with higher characteristic temperatures of threshold current (T₀) and slope efficiency (T₁). Furthermore, the co-doped laser can maintain stable continuous-wave ground-state lasing up to a high temperature of 115°C. These results prove the great potential of co-doping technique for enhancing silicon-based QD laser performances towards lower power consumption, higher temperature stability, and higher operating temperature, to boost the development of high-performance silicon photonic chips.

We report on significantly enhanced performances of 1.3 μm InAs/GaAs quantum dot (QD) lasers by spatially separated dual-doping, including p-type modulation doping in barrier layers and n-type direct doping in QDs simultaneously. The QD lasers are a ridge waveguide of 6 × 1000 μm² with uncoated facets, whose active region consists of eight stacked InAs QD layers. Compared with the conventional single p-type modulation doped (p-doped) QD laser, the dually doped QD laser achieves a reduced threshold current from 51.07 to 43 mA, an increased single-sided slope efficiency from 0.18 to 0.25 W/A at 25 °C, and an increased characteristic temperature T₀ from 654 to 7917 K between 15 and 85 °C. Furthermore, the continuous wave output power of the dually doped QD laser exceeds 20 mW without any attenuation at 85 °C, whereas that of the p-doped one appears to be saturated at 14.08 mW. The results presented here have important implications for realizing high-performance QD lasers emitting at 1.3 μm to various applications.

Self-flattened and low-resistance Al-doped ZnO (ZnO:Al) thin films were developed by sol–gel process, for providing a versatile transparent conducting oxide material that enables the growth of high-quality photoactive layers and enhancement in light absorption by intensifying light-scattering simutaneously. The electrical, optical, and structural characteristics of the sol–gel derived ZnO:Al thin film was evaluated by comparing with the B-doped ZnO (ZnO:B) fabricated by the metalorganic chemical vapor deposition method and ZnO:Al fabricated by the radio-frequency magnetron sputtering deposition method. This sol–gel derived ZnO:Al thin film shows the c-axis oriented wurtzite structure, a resistivity of 9.89 × 10−4 Ω·cm, and smoother surface morphology and larger figure of merit σ/α than the vacuum-technique derived ZnO thin film with similar thickness. This low resistivity was achieved by optimizing the Al doping concentration and annealing process. Employed as the front electrode, it enabled a better device performance of hydrogenated amorphous Si single-junction solar cells with respect to the ZnO:B thin film with similar thickness by improving the V$_{oc}$ and fill factor (FF). The dark J–V characteristics of these devices were analyzed to investigate the mechanism of V$_{oc}$ and FF improvement. These results suggest a promising candidate for the transparent electrode of superstrate-type thin-film solar cells.