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1 μm thick Si solar cells based on nanocone grating (NCG) with height of 100-800 nm and period of 100, 500, and 800 nm are numerically investigated through reflectivities, absorption enhancement factors, absorption spectra, optical generation rates, ultimate efficiencies, and diffraction angles. Compared with the planar Si solar cell, absorption enhancement are observed in any solar cells with NCG surface. Their absorption enhancement mechanism varies with the incident wavelength range. When incident wavelength λ < 500 nm, antireflection of their front surface dominates the absorption enhancement behavior due to their stronger absorption coefficients. When 600 nm > λ > 500 nm, even though the absorption enhancement is still dominated by antireflection of the front surface, cavity-resonance effect and guided-mode excitation induced by high order diffraction start to make contribution. When λ > 600 nm, the contribution of guided-mode excitation induced by lower-order diffraction becomes larger and larger once the diffraction angle is larger than its critical angle. For the structure with P = 100 nm, high-order diffraction cut-off at the longer wavelength range is the main reason of its lower absorption enhancement and ultimate conversion efficiency. For P = 800 nm, the lower absorption enhancement and ultimate efficiency is also observed due to the high reflection loss and mode leakage induced by 1st order diffraction where its diffraction angle is lower than its critical angle. Higher absorption and ultimate conversion efficiencies are achieved in P = 500 nm due to the good balance between antireflection performance and guide-mode excitation induced by the high order diffraction is achieved. Moreover, such absorption enhancement is closely related with its height of NCG gratings. Reflection loss reduction, the interaction volume reduction between the incident light and Si material, and higher photon density in NCG structure coexists with H increasing, which results in absorption enhancement in P = 500 nm and P = 800 nm, but absorption reduction in P = 100 nm where high order diffraction cut-off. Based on these analysis, we do believe that high absorption and ultimate conversion efficiency should be achieved in NCG-based solar cells where both the lower reflection in short wavelength domain and guide-mode excitation induced by 1st and 2nd diffraction in longer wavelength domain can be achieved. According to this rule, the optimized structure is NCG with P = 559 nm and H = 500 nm, by which, the highest optical generation rate of 536.57 × 104 W/cm3 and ultimate efficiency of 28.132% are achieved. Such analysis should benefit the design of the thin film solar cells with nano-structured diffraction gratings. [ABSTRACT FROM AUTHOR]

We have investigated phase separation, silicon nanocrystal (Si NC) formation and optical properties of Si oxide (SiOx, 0x films were deposited by plasma-enhanced chemical vapor deposition at different nitrous–oxide/silane flow ratios. The physical and optical properties of the SiOx films were studied as a result of high-vacuum annealing and thermal oxidation. X-ray photoelectron spectroscopy (XPS) reveals that the as-deposited films have a random-bonding or continuous-random-network structure with different oxidation states. After annealing at temperatures above 1000 °C, the intermediate Si continuum in XPS spectra (referring to the suboxide) split to Si peaks corresponding to SiO2 and elemental Si. This change indicates the phase separation of the SiOx into more stable SiO2 and Si clusters. Raman, high-resolution transmission electron microscopy and optical absorption confirmed the phase separation and the formation of Si NCs in the films. The size of Si NCs increases with increasing Si concentration in the films and increasing annealing temperature. Two photoluminescence (PL) bands were observed in the films after annealing. The ultraviolet (UV)-range PL with a peak fixed at 370–380 nm is independent of Si concentration and annealing temperature, which is a characteristic of defect states. Strong PL in red range shows redshifts from ∼600 to 900 nm with increasing Si concentration and annealing temperature, which supports the quantum confinement model. After oxidation of the high-temperature annealed films, the UV PL was almost quenched while the red PL shows continuous blueshifts with increasing oxidation time. The different oxidation behaviors further relate the UV PL to the defect states and the red PL to the recombination of quantum-confined excitions. [ABSTRACT FROM AUTHOR]

A GaInP/AlGaInP multiple quantum well laser structure was grown by low-pressure metalorganic chemical vapor deposition with tertiarybutylarsine and tertiarybutylphosphine. Laser diodes fabricated from this structure lased at room temperature. Photoluminescence (PL) measurements were performed from 10 to 230 K. The PL energy increased with temperature from 10 to 70 K and decreased above 70 K. The former was attributed to thermal activation of trapped carriers due to localization in the quantum wells, while the latter was attributed to temperature-induced band-gap shrinkage. The PL intensity as a function of temperature was fitted by employing two nonradiative recombination mechanisms with good agreement, resulting in two activation energies that correspond to losses of photogenerated carriers to nonradiative centers. © 2003 American Institute of Physics. [ABSTRACT FROM AUTHOR]

We report the technique of controlled group V quantum well intermixing (QWI) in a compressively strained In[SUB0.76]Ga[SUB0.24]As[SUB0.85]P[SUB0.15]/In[SUB0.76]Ga[SUB0.24]As[SUB0 .52]P[SUB0.48] multiquantum well laser structure and its application to the fabrication of two-section tunable lasers. The blueshift of the band-gap energy was enhanced by capping the samples with films of SiO[SUB2] or low-temperature grown InP, while suppressed by a Si[SUBx]N[SUBy] film with a refractive index of about 2.1. Spatially selective band-gap tuning was achieved by patterning the dielectric film into dot and strip arrays with different surface coverage. Time-of-flight secondary ion mass spectra showed that the enhanced blueshift was caused by the interdiffusion of group V atoms between the quantum wells and barriers. A group V interstitial interdiffusion mechanism is proposed for the sample capped with SiO[SUB2] and this is supported by the even more efficient intermixing induced by low-temperature InP, which contains a high concentration of excess phosphorus. A two-section tunable laser operating around 1.55 μm was fabricated using this QWI technology. A tuning range of about 10 nm was demonstrated by simply changing the current injected into the phase tuning section. [ABSTRACT FROM AUTHOR]

The material and optical properties of the GaAs/AlxGa1-xAs/Ge structures grown by metalorganic chemical vapor deposition were examined and found to be dependent of the Al content x. SIMS and PL measurements show that the 10 nm AlxGa1-xAs buffer layer with x = 0.3 and 0.6 are equally effective in suppressing the outdiffusion of Ge, whereas x = 1.0 gives the most abrupt interface. The best morphology with surface rms of 0.3 nm is obtained in the structure with x = 0.3 buffer layer. Analysis on change of strain in the AlxGa1-xAs buffer layer suggests that the compressive strain at the AlxGa1-xAs-GaAs interface is compensated by the tensile strain at the Ge-AlxGa1-xAs interface when x ∼ 0.3. AlxGa1-xAs lattice matched to Ge is crucial for better result in surface morphology, but higher Al content is preferred for eliminating the interdiffusion of atoms at the heterointerface. [ABSTRACT FROM AUTHOR]

GaInP/AlGaInP triple quantum well (TQW) lasers, grown by metalorganic chemical vapor deposition (MOCVD) using tertiarybutylarsine (TBAs) and tertiarybutylphosphine (TBP), were fabricated with a pulsed anodic oxidation (PAO) process. The devices worked at room temperature (RT) with the lowest threshold current density (Jth) of 1.5 kA/cm2 ever reported for GaInP/AlGaInP lasers grown using TBAs and TBP. Temperature dependent (35–250 K) electroluminescence (EL) study of the GaInP/AlGaInP laser diode showed almost the same luminescence quenching behavior at a high temperature region (120–250 K), independent of the injection current (100–150 mA). A model involving a nonradiative recombination mechanism was presented to interpret the EL quenching behavior over the experimental temperature range. The nonradiative recombination centers in the Al-containing barrier or cladding layer are believed to contribute to the loss of carriers via nonradiative recombination. [ABSTRACT FROM AUTHOR]

Examines the optimization of pulsed anodic oxidation for the fabrication of AlGaInP laser diodes grown with tertiarybutylarsine and tertiarybutylphosphine. Lasing characteristics of InGaP/InGaAIP visible lasers grown by metalorganic chemical vapor deposition with tertiarybutylphospine; Fabrication of high-performance InGaAsN RWG lasers with pulse anodic oxidation; Effects of thermally grown native oxides on the luminescence properties of compound semiconductors.

The authors report a technology to make a distributed Bragg reflector laser with buried dielectric grating and band gap tuned reflector region. The Bragg reflector is constructed by high coupling coefficient gratings made of SiO2 and InP. The band gap of the reflector is blueshifted by self-aligned quantum well intermixing using the buried SiO2 grating itself. The photoluminescence peak wavelength can be shifted by ∼45 meV for the quantum well sample covered by SiO2 grating compared to thermal shift only at annealing temperature of 800 °C for 100 s. The enhanced interdiffusion is caused by the P vacancies generated at SiO2 and InP interfaces as proved by secondary ion mass spectroscopy. [ABSTRACT FROM AUTHOR]

Inductively coupled argon plasma-enhanced intermixing of InAs/InP quantum dots grown on InP substrate is investigated. Intermixing is promoted by the near-surface defects generated by plasma exposure in annealing at a temperature of 600 °C for 30 s. The annealing results in a maximum differential band-gap blueshift of 106 nm but a thermal shift of only 10 nm. Band-gap halftones are obtained by controlling the amount of near-surface defects via wet chemical etching on the plasma-exposed InP cap layer. No degradation of quantum-dot crystal quality due to the process has been observed as evidenced by photoluminescence intensity. [ABSTRACT FROM AUTHOR]

In this letter, we report the observation of the longitudinal mode grouping effect in the InGaAsP/InP multiquantum-well ridge waveguide laser. Two mode groups were observed and showed different behaviors with the changing of the injection current. The higher order lateral modes and the current spreading in the ridge waveguide structure is proposed to be responsible for this mode grouping phenomena. A one-step quantum-well intermixing process using the SiO2 electrical isolation layer itself was introduced and proved to be effective in improving the lateral electrical and optical confinement in a ridge waveguide laser structure as well as eliminating the mode grouping. [ABSTRACT FROM AUTHOR]

In this letter, we report on temperature-dependent anti-Stokes photoluminescence (ASPL) at an interface between partially ordered GaInP[sub 2] epilayer and GaAs substrate. It is found that the intensity of the ASPL depends strongly on temperature accompanying with a clear blueshift in energy. A localized-state luminescence model was employed to quantitatively interpret temperature dependence of the ASPL. Excellent agreement between the theory and experiment was obtained. Radiative recombination mechanism of the up-converted carriers was discussed. © 2004 American Institute of Physics. [ABSTRACT FROM AUTHOR]