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The unique degradation behavior of a tunneling field-effect transistor (TFET) under hot-carrier injection (HCI) stress has been previously investigated. However, while the source side (p+/p junction) of degradation (due to HCI stress) has been extensively studied, the drain side (p/n+ junction) has not been investigated yet. Our study revealed that both bulk oxide and interfacial layer degradation occurred at the drain side, while an interfacial layer degradation was dominant at the source side at 300 K. This evidences a unique degradation mechanism of the tunneling FET.

GaAs/GaInAs multiple-quantum-well (MQW) shells having different GaInAs shell width formed on the surface of self-catalyzed GaAs core nanowires (NWs) are grown on (100) Si substrate using molecular beam epitaxy. The photoluminescence emission from GaAs/GaInAs MQW shells and the carrier lifetime could be varied by changing the width of GaInAs shell. Time-resolved photoluminescence measurements showed that the carrier lifetime had a fast and slow decay owing to the mixing of wurtzite and zinc-blende structures of the NWs. Furthermore, strain relaxation caused the carrier lifetime to decrease beyond a certain thickness of GaInAs quantum well shells.

We report on advanced types of coverglasses, which include the hierarchical micro- and subwavelength-structured surfaces for improved absorption efficiency of photovoltaic modules. Prism-shaped microstructures (PSMSs) help eliminate the optical shading caused by the metal grid of solar cells. The subwavelength structures (SWSs) with a tapered shape behave as a refractive index matching layer to reduce the surface reflection at the interface of air and coverglass. The geometries of the PSMSs and SWSs were designed by ray-tracing and the rigorous coupled-wave analysis method simulations, respectively, which provided the design guidelines. The PSMSs and SWSs were fabricated by a simple two-step process consisting of an isotropic wet etching process with hydrofluoric acid solution using a SiN x mask and a self-masked dry etching process, respectively. A hybrid patterned coverglass incorporating the PSMSs with SWSs were mounted on GaInP/(In)GaAs/Ge triple-junction solar cells with a precise alignment process. The measured power conversion efficiency of the subreceiver module with the patterned glass reached 32.97% for 1 sun, which is 11.19% higher compared with a subreceiver module with a flat coverglass.

We present a single-material titanium oxide (TiO2) bi-layer antireflection coating (ARC) produced using oblique angle deposition for improving the power conversion efficiency (PCE) of III–V compound semiconductor triple-junction (TJ) solar cells. Experimental demonstration of the porous TiO2 layers and optical modelling by rigorous coupled-wave analysis indicate that bi-layer TiO2 could be used as universal ARC for all known TJ stacks with various material combinations. The optimum TiO2 bi-layer ARC produced on a Ga0.5In0.5P/GaAs/Ge TJ solar cell exhibits considerably enhanced PCE of 31.6%, which is higher than that of the cells without ARC (23.8%) and with TiO2 single-layer ARC (29.1%). Incident angle-dependent device characteristics of the fabricated TJ solar cells are also discussed.

In general, to realize full color, inorganic light-emitting diodes (LEDs) are diced from respective red-green-blue (RGB) wafers consisting of inorganic crystalline semiconductors. Although this conventional method can realize full color, it is limited when applied to microdisplays requiring high resolution. Designing a structure emitting various colors by integrating both AlGaInP-based and InGaN-based LEDs onto one substrate could be a solution to achieve full color with high resolution. Herein, we introduce adhesive bonding and a chemical wet etching process to monolithically integrate two materials with different bandgap energies for green and red light emission. We successfully transferred AlGaInP-based red LED film onto InGaN-based green LEDs without any cracks or void areas and then separated the green and red subpixel LEDs in a lateral direction; the dual color LEDs integrated by the bonding technique were tunable from the green to red color regions (530–630 nm) as intended. In addition, we studied vertically stacked subpixel LEDs by deeply analyzing their light absorption and the interaction between the top and bottom pixels to achieve ultra-high resolution.

Nitrogen flow rate is one of the important growth parameters for the growth of group-III nitride nanowires in plasma-assisted molecular beam epitaxy. However, nitrogen flow rate has received less attention compared to the group-III metal fluxes since its effects are not as prominent as that of the metal fluxes. In this study, we investigated the effects of nitrogen flow rate on the morphology and composition of AlGaN nanowires. Reducing the nitrogen flow rate improved the structural uniformity and increased the Al composition. We present a composition change model and show that excess nitrogen suppresses Ga desorption by recombining the Ga atoms, thereby causing a change in the composition of AlGaN. It was confirmed that the influence of the nitrogen flow rate on the Al composition varied with the growth temperature. These results provide insights into the role of nitrogen flow rate on the growth of AlGaN nanowires and suggest that more sophisticated growth control is possible by considering the nitrogen flow rate.

High-performance GaAs tunnel diodes (TDs) are fabricated by using Si delta-doping technique. The GaAs TDs exhibited a high peak tunnel-current density of 2,735 A/cm2 and low specific resistivity of 1.46 × 10−4 Ωcm2. However, the performance of the GaAs TDs deteriorated once the amount of Si delta doping exceeded a certain limit, which has been rarely reported elsewhere. Detailed analyses and numerical simulations of GaAs TDs with various amounts of Si delta doping prove that Si amphoteric behavior governs the performance limit. GaAs TDs with precisely controlled Si delta doping are suitable for cutting-edge tandem solar cell applications.

We devised directionally controllable THz emission sources based on lateral composition modulation (LCM) structures. LCM structures were composed of In-rich Ga0.47In0.53P and Ga-rich Ga0.51In0.49P layers whose period was in quantum scale of ~`5 nm. The inherent type II band alignment in these structures leads to electron-hole (e-h) separation and plays a key role in generating later- ally polarized dipole ensembles, thus concomitantly emitting enhanced transmissive THz waves as compared to bulk sample. On the other hand, in lateral geometry, changes in THz fields between LCM and bulk structures turned out to negligible since the vertical electronic diffusion was allowed in both samples.

We report changes at the interface between Ga-rich/In-rich GaInP vertical slabs in laterally composition modulated (LCM) GaInP as a function of the V/III ratio. The photoluminescence exhibits satellite peaks, indicating that the parasitic potential between the GaInP vertical slabs disappears as the V/III ratio decreases. However, a high V/III ratio leads to an abrupt interface, increasing the parasitic potential because of the phosphorus-amount-dependent diffusion of group-III atoms during growth. These results suggest that the V/III ratio is an important parameter that must be wisely chosen in designing optoelectronic devices incorporating LCM structure.

Double-hetero structure lateral composition modulated (LCM) GaInP and sandwiched LCM GaInP having the same active layer thickness were grown and their optical properties were compared. Sandwiched LCM GaInP showed robust optical properties due to periodic potential nature of the LCM structure, and the periodicity was undistorted even for thickness far beyond the critical layer thickness. A thick LCM GaInP structure with undistorted potential that could preserve the properties of native LCM structure was possible by stacking thin LCM GaInP structures interspaced with strain compensating GaInP layers. The sandwiched structure could be beneficial in realizing the LCM structure embedded high efficiency solar cells.

We report the performance enhancement of a molecular beam epitaxy grown GaAs tunnel diode embedded with InAs quantum dots (QDs) for tandem solar cell application, and characterization of tunnel diodes embedded with InAs QDs grown with different growth parameters. Prior to the growth and fabrication of the tunnel diode, InAs QDs were grown under different growth durations and temperatures. The InAs QD samples grown in a temperature range from 480 to 520 °C for a duration of 32 s showed the highest areal fill fraction by InAs QDs. Tunnel diodes embedded with InAs QDs that were grown at various growth conditions were fabricated and characterized. We found that the tunnel diode embedded with InAs QD grown at 520 °C showed the highest peak tunnel current density among all the samples. The enhanced performance of the InAs QD embedded tunnel diode is attributed to the large areal fill fraction produced by the presence of large InAs QDs having high density, which are formed at sufficiently high growth temperature and long growth duration.

GaAs tunnel diodes (TDs) embedded with an InAs quantum dot (QD) layer were grown and their performance was compared with that of TDs without a QD layer. The TDs embedded with a QD layer showed enhanced peak tunnel current density and lower differential resistivity at zero bias compared with the TDs without a QD layer. The samples were then annealed to mimic the overlayer growth process. It was found that the performance degradation after annealing was smaller for the QD-layer-embedded TDs. The improved characteristics of the QD-layer-embedded GaAs TDs make them advantageous for interconnecting unit cells in tandem solar cells.

We report the enhancement of the minority carrier lifetime of GaInP with a lateral composition modulated (LCM) structure grown using molecular beam epitaxy (MBE). The structural and optical properties of the grown samples are studied by transmission electron microscopy and photoluminescence, which reveal the formation of vertically aligned bright and dark slabs corresponding to Ga-rich and In-rich GaInP regions, respectively, with good crystal quality. With the decrease of V/III ratio during LCM GaInP growth, it is seen that the band gap of LCM GaInP is reduced, while the PL intensity remains high and is comparable to that of bulk GaInP. We also investigate the minority carrier lifetime of LCM structures made with different flux ratios. It is found that the minority carrier lifetime of LCM GaInP is ∼37 times larger than that of bulk GaInP material, due to the spatial separation of electrons and holes by In-rich and Ga-rich regions of the LCM GaInP, respectively. We further demonstrate that the minority carrier lifetime of the grown LCM GaInP structures can easily be tuned by simply adjusting the V/III flux ratio during MBE growth, providing a simple yet powerful technique to tailor the electrical and optical properties at will. The exceptionally high carrier lifetime and the reduced band gap of LCM GaInP make them a highly attractive candidate for forming the top cell of multi-junction solar cells and can enhance their efficiency, and also make them suitable for other optoelectronics devices, such as photodetectors, where longer carrier lifetime is beneficial.

We report the numerical analysis of p-GaAs/n-GaAs tunnel junction employing InAs as the intermediate layer at the junction. Incorporation of this intermediate layer introduces an intermediate level at the junction bandgap leading to enhanced tunneling of carriers. By doing so, we obtain a two order of enhancement in the tunnel current. Furthermore, the performance of GaInP/GaAs dual-junction solar cells using the TJ with InAs intermediate layer is calculated under concentrated suns condition and it shows a conversion efficiency exceeding 30% under 1800 suns condition.