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We have achieved the first monolithically integrated triple-junction InGaP/GaAsP/SiGe solar cell on Si substrate, achieving an adjusted efficiency of 20% AM0 1-sun. The practical achievable maximum AM0 efficiency for the optimal cell near this lattice constant is 39%. The combination of this high efficiency with the ability to process such cells on larger area lower-cost silicon substrates motivates...
Silicon-based tandem solar cells are desirable as a high efficiency, economically viable approach to one sun or low concentration photovoltaics. We present an approach to wafer bonded III–V/Si solar cells using amorphous indium zinc oxide (IZO) as an interlayer. We investigate the impact of a heavily doped III–V contact layer on the electrical and optical properties of bonded test samples, including...
As crystalline silicon solar cells may be approaching efficiency limits, a promising approach to further efficiency gains is a stacked, tandem system consisting of silicon and below silicon band gap cells capable of utilizing a larger range of the solar spectrum. In this work, we analyze a textured silicon cell with coatings optimized to transmit below band gap photons. For the first time, our model...
In this paper we present theoretical analysis for upper efficiency limit of a novel 2 terminal dual junction stepcell. Results show that step cell design relaxes bandgap requirements for efficient tandem cell. While conventional tandem cell with optimized bandgap combination (1.64 / 0.96 eV) has the highest efficiency (45.78 %), the step-cell design provides significant efficiency improvement for...
Employing a 8 band k.p solver, the self-consistent band structure of the rectangular IIIV nanowires (NW) has been calculated. It is shown that the strong confinement combined with the band nonparabolicity will considerably change the effective masses and the band gap. The mass tensor elements get heavier than the bulk values and improve the density of state (DOS) and centroid capacitance accordingly,...
Efficiency of ultraviolet (UV) and Deep UV LEDs are mainly hindered by poor dopant ionization in wide bandgap AlGaN. Polarization induced doping via composition grading has been used to increase the amount of ionized dopants [1, 2]. Composition gradient over the full composition range is limited by the small critical thickness of the epitaxial graded layer in planar thin films. However, nanowires...
Based on the experience with silicon (Si) devices, some characteristics of silicon carbide (SiC) devices are likely to be misunderstood. In this paper, studies on channel mobility, time dependent dielectric breakdown (TDDB), and negative bias temperature instability (NBTI) in 4H-SiC MOSFETs are reviewed. Through the discussions, it is indicated that SiC-based models, such as local band gap modulation,...
We have demonstrated high performance operation of planar-type tunnel field-effect transistors (TFETs) using Ge/ III–V materials. Tensile strain in Si channels combined with the Ge source can enhance the tunneling current because of the reduced effective bandgap. The fabricated Ge/sSOI (1.1 %) TFETs show high Ion/Ioff ratio over 107 and steep minimum subthreshold slope (SS) of 28 mV/dec. It is found...
We developed a low thermal budget NVM to exhibit a faster operation speed (1 μs) and a lower operation voltage (+9 V) with reliable retention and endurance. Accordingly, the NVM fabrication processes reduce the power consumption, and are compatible with the CMOS technology, facilitating the realization of monolithic SRAM/NVM in the future.
In conclusion, we demonstrated the fabrication and I–V characteristics of HfS2 FETs. For the channel thickness of less than 7.5 nm, a clear saturation behavior and drain current of 0.2 µA/µm were observed with reasonably good on/off current ratio. These results provide basic knowledge of HfS2 as a channel material for FET.
Here we present modeling results on crystalline Si (c-Si)/amorphous Si (a-Si) heterojunction solar cells using a physical simulation which includes various models for the defect states in the a-Si barriers, as well as explicit models for the ITO emitter contact. We investigate the impact of the band offsets and barrier heights of the a-Si/c-Si interface, particularly in terms of the open circuit voltage...
We present a concept of a split tandem photovoltaic window, where the larger wavelengths solar radiations are sent towards horizontal silicon solar cells while short wavelength solar radiations are directed on transparent large band gap solar cells, either dye-sensitized or organic solar cells (DSSC and OSC respectively). We first evaluate the expected enhancement in them of conversion efficiency...
With the advent of high-bandgap perovskites, the opportunity now exists to make tandems with perovskites on top of silicon. We have prototyped a mechanically stacked tandem, achieving 17.9% certified efficiency using a perovskite cell with a silver nanowire mesh electrode. We have also prototyped a monolithically integrated tandem on silicon, with the two subcells electronically connected by band-to-band...
We investigate the growth, microstructure and device characteristics of 1.71eV bandgap GaAs0.76P0.24 solar cells grown on Si substrates using SiyGe1−y graded buffers. Our optimized growth conditions suppress defect nucleation at the GaAsP/SiGe heterointerface and enable the demonstration of single junction solar cells with a threading dislocation density of 3.4×106 cm−2, a 3× reduction compared to...
Recent development of Si-Ge-Sn ternary alloys offers an alternative to 1.0 eV bandgap materials for multijunction solar cells. Main advantages of these alloys are tunable gap energy and variable lattice parameter, which can be fitted into the existing designs, thus resulting in a lattice matched solution. Recent growth, optical and structural results from Si-Ge-Sn with ∼ 1 eV gaps and lattice matched...
After successful fabrication of graphene, atomically thin two-dimensional (2D) materials have attracted a growing interest due to its intriguing novel properties and promising applications [1-3]. However, the intrinsic zero band gap of graphene hinders its applications in low-dimensional spintronics. Recently, few-layer black phosphorus (black phosphorene), has been successfully isolated by mechanical...
Recently, it has been demonstrated that CPP-GMR can be significantly boosted by incorporating new ferromagnetic (FM) full Heulser alloy into spin valve nano-structures[1-4]. Experimental results for two types of non-magnetic spacers (i) (100) textured Ag in combination with FM full Heusler alloys Co2MnSi, Co2Fe(Si-Al) [1], Co2(Mn-Fe)Si (70 % MR and DRA of about 12 mW-mm2) [2] and (ii) non-magnetic...
We report an approach to suppress anchor loss in thin-film piezoelectric-on-silicon (TPoS) micromechanical (MEMS) resonators by patterning 2D phononic crystals (PnCs) externally on the anchors. The PnCs serve as a frequency-selective reflector for outgoing acoustic waves through the tethers of the TPoS resonator. According to our experimental results, combining the PnCs with the conventional TPoS...
Combining quantum well intermixing and multiple die bonding a broadband superluminescent III-V on silicon LED was realized. Balancing four LEDs with different band gaps resulted in 292nm 3dB bandwidth and an on-chip power of −8dBm.
Room temperature electroluminescence (EL) from Ge/Ge0.92Sn0.08/Ge double heterostructure light-emitting diodes has been observed. Spectrum measurements show an emission peak at 0.601eV, which is attributed to direct bandgap transition.
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