Picosecond internal Q-switching mode correlates with laser diode breakdown voltage

The record picosecond power density recently achieved with a current-pumped laser diode turned our attention to a still unexplained 50-year-old phenomenon termed “internal Q-switching”. The correlation found experimentally here between the relatively high breakdown voltage (～5–11 V) in a heavily doped single-heterostructure laser diode and its high-power picosecond lasing provides a means for solving the puzzle. Together with the experimental fact that picosecond lasing occurs from the p-n junction, this implies that internal Q-switching is determined by the compensated layer rather than by “traditional” single-heterostructure waveguide. This finding is valid for various growth technologies independently of whether the high break-down voltage and picosecond lasing are achieved by exact compensation of shallow donors by shallow acceptors, or by doping profile gradients.     

Time-Resolved Photoluminescence of InGaAs Nanostructures Different in Quantum Dimensionality

Semiconductors - The time-resolved photoluminescence of quantum-confined InGaAs heterostructures grown on GaAs substrates is studied by time-correlated single photon counting. The heterostructures...     

Increasing the quantum efficiency of InAs/GaAs QD arrays for solar cells grown by MOVPE without using strain‐balance technology

Research into the formation of InAs quantum dots (QDs) in GaAs using the metalorganic vapor phase epitaxy technique is presented. This technique is deemed to be cheaper than the more often used and studied molecular beam epitaxy. The best conditions for obtaining a high photoluminescence response, indicating a good material quality, have been found among a wide range of possibilities. Solar cells with an excellent quantum efficiency have been obtained, with a sub‐bandgap photo‐response of 0.07 mA/cm² per QD layer, the highest achieved so far with the InAs/GaAs system, proving the potential of this technology to be able to increase the efficiency of lattice‐matched multi‐junction solar cells and contributing to a better understanding of QD technology toward the achievement of practical intermediate‐band solar cells. Copyright © 2016 John Wiley & Sons, Ltd.     

Study of minority carrier diffusion lengths in photoactive layers of multijunction solar cells

A technique for determining a minority carrier’s diffusion length in photoactive III–V layers of solar cells by approximating their spectral characteristics is presented. Single-junction GaAs, Ge and multi-junction GaAs/Ge, GaInP/GaAs, and GaInP/GaInAs/Ge solar cells fabricated by hydride metal-organic vapor-phase epitaxy (H-MOVPE) have been studied. The dependences of the minority carrier diffusion length on the doping level of p-Ge and n-GaAs are determined. It is shown that the parameters of solid-state diffusion of phosphorus atoms to the p-Ge substrate from the n-GaInP nucleation layer are independent of the thickness of the latter within 35–300 nm. It is found that the diffusion length of subcells of multijunction structures in Ga(In)As layers is smaller in comparison with that of single-junction structures.     

Evaluation of the Impact of Surface Recombination in Microdisk Lasers by Means of High-Frequency Modulation

Semiconductors - Microdisk lasers 10–30 μm in diameter operating at room temperature without thermal stabilization and with an active region based on nanostructures of hybrid...     

Germanium subcells for multijunction GaInP/GaInAs/Ge solar cells

Photovoltaic converters based on n-GaInP/n-p-Ge heterostructures grown by the OMVPE under different conditions of formation of the p-n junction are studied. The heterostructures are intended for use as narrow-gap subcells of the GaInP/GaInAs/Ge three-junction solar cells. It is shown that, in Ge p-tn junctions, along with the diffusion mechanism, the tunneling mechanism of the current flow exists; therefore, the two-diode electrical equivalent circuit of the Ge p-n junction is used. The diode parameters are determined for both mechanisms from the analysis of both dark and “light” current-voltage dependences. It is shown that the elimination of the component of the tunneling current allows one to increase the efficiency of the Ge subcell by ∼1% with conversion of nonconcentrated solar radiation. The influence of the tunneling current on the efficiency of the Ge-based devices can be in practice reduced to zero at photogenerated current density of ∼1.5 A/cm² due to the use of the concentrated solar radiation.     

A Micro Optocoupler Based on a Microdisk Laser and a Photodetector with an Active Region Based on Quantum Well-Dots

Technical Physics Letters - The feasibility of detecting the emission of a microdisk laser with a diameter of 23 μm with an active region based on InGaAs/GaAs quantum well-dots using a nearby...     

Lasers Based on Quantum Well-Dots Emitting in the 980- and 1080-nm Optical Ranges

Technical Physics Letters - The main characteristics of edge-emitting lasers with active regions based on nanoheterostructures of a new type—quantum well-dots (QWDs) operating at various...     

Module of Laser-Radiation (λ = 1064 nm) Photovoltaic Converters

Semiconductors - The results of a study and the development of a module designed for energy transmission via atmospheric channels are presented. The four-cell module based on single-junction...     

Density Control of InP/GaInP Quantum Dots Grown by Metal-Organic Vapor-Phase Epitaxy

We investigated structural and emission properties of self-organized InP/GaInP quantum dots (QD) grown by metal organic chemical vapor deposition using an amount of deposited In from 7 to 2 monolayers (ML). In the uncapped samples, using atomic force microscopy (AFM), we observed lateral sizes of 100–200 nm, together with a bimodal height distribution having maxima at ～5 and ～15 nm, which we denoted as QDs of type A and B, respectively; and reduction of the density of the type-B dots from 4.4 to 1.6 μm^–2. The reduction of the density of B-type dots were observed also using transmission electron microscopy of the capped samples. Using single dot low-temperature photoluminescence (PL) spectroscopy we demonstrated effects of Wigner localization for the electrons accumulated in these dots.