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In this paper, we study the behavior of photoexcited carriers in GaAs wafers containing self-assembled InAs quantum dots (QDs). These samples were designed and grown to be employed as photoconductive antennae for terahertz (THz) generation. The implanted QDs serve to shorten the overall carrier lifetime and enable pumping with lasers operating at wavelengths between 1 μ m and 1.3 μ m. Optical pump-THz probe measurements reveal carrier lifetime shortening for higher pump powers in the unbiased antennae due to increased carrier capture via Auger relaxation. This phenomenon significantly broadens the THz spectra from QD-based PCAs and explains the increased THz intensity at higher frequencies presented earlier. [ABSTRACT FROM AUTHOR]

The defect properties of InGaAsN dilute nitrides grown as sub-monolayer digital alloys (SDAs) by molecular beam epitaxy for photovoltaic application were studied by space charge capacitance spectroscopy. Alloys of i-InGaAsN (Eg = 1.03 eV) were lattice-matched grown on GaAs wafers as a superlattice of InAs/GaAsN with one monolayer of InAs (<0.5 nm) between wide GaAsN (7–12 nm) layers as active layers in single-junction solar cells. Low p-type background doping was demonstrated at room temperature in samples with InGaAsN layers 900 nm and 1200 nm thick (less 1 × 1015 cm−3). According to admittance spectroscopy and deep-level transient spectroscopy measurements, the SDA approach leads to defect-free growth up to a thickness of 900 nm. An increase in thickness to 1200 nm leads to the formation of non-radiative recombination centers with an activation energy of 0.5 eV (NT = 8.4 × 1014 cm−3) and a shallow defect level at 0.20 eV. The last one leads to the appearance of additional doping, but its concentration is low (NT = 5 × 1014 cm−3) so it does not affect the photoelectric properties. However, further increase in thickness to 1600 nm, leads to significant growth of its concentration to (3–5) × 1015 cm−3, while the concentration of deep levels becomes 1.3 × 1015 cm−3. Therefore, additional free charge carriers appearing due to ionization of the shallow level change the band diagram from p-i-n to p-n junction at room temperature. It leads to a drop of the external quantum efficiency due to the effect of pulling electric field decrease in the p-n junction and an increased number of non-radiative recombination centers that negatively impact lifetimes in InGaAsN. [ABSTRACT FROM AUTHOR]

A laser-driven semiconductor switch (LDSS) employing silicon (Si) and gallium arsenide (GaAs) wafers has been used to produce nanosecond-scale pulses from a 3 μs, 110 GHz gyrotron at the megawatt power level. Photoconductivity was induced in the wafers using a 532 nm laser, which produced 6 ns, 230 mJ pulses. Irradiation of a single Si wafer by the laser produced 110 GHz RF pulses with a 9 ns width and >70% reflectance. Under the same conditions, a single GaAs wafer yielded 24 ns 110 GHz RF pulses with >78% reflectance. For both semiconductor materials, a higher value of reflectance was observed with increasing 110 GHz beam intensity. Using two active wafers, pulses of variable length down to 3 ns duration were created. The switch was tested at incident 110 GHz RF power levels up to 600 kW. A 1-D model is presented that agrees well with the experimentally observed temporal pulse shapes obtained with a single Si wafer. The LDSS has many potential uses in high power millimeter-wave research, including testing of high-gradient accelerator structures. [ABSTRACT FROM AUTHOR]

Research to synthesize a high-quality GaAs film on an inexpensive substrate has been continuing for decades in the quest to develop a solar cell that achieves both high efficiency and low-cost. Here, we applied a large-grained Ge layer on glass, formed by Al-induced layer exchange, to an epitaxial template for a GaAs film. The GaAs film, grown epitaxially from the Ge seed layer at 520 °C, became a pseudosingle crystal (grain size > 100 μm) with high (111) orientation. Reflecting the large grain size, the internal quantum efficiency reached 70% under a bias voltage of 1.0 V. This value approaches that of a simultaneously formed GaAs film on a single-crystal Ge wafer and is the highest for a GaAs film synthesized on glass at a low temperature. The application of a Ge seed layer formed by layer exchange offers excellent potential to develop high-efficiency thin-film solar cells with III–V compound semiconductors based on low-cost glass substrates. [ABSTRACT FROM AUTHOR]

In this work, we report on simultaneously mapping of the thermal diffusivity and effective infrared absorption coefficient of GaAs wafer using infrared lock-in thermography. The phase images were extracted from the temperature modulation of the investigated surface at different excitation frequencies, by applying the lock-in detection for each pixel of the recorded image. The resulting images were analyzed using the thermal wave model in the transmission configuration. The thermal diffusivity and the effective infrared absorption coefficient were estimated from the best fit of the theoretical model to the experimental data applied for each pixels of the phase images. Finally, we used different image filters to decrease the estimation errors of the parameters and to enhance the quality of the images. The results demonstrate that the lock-in thermography technique in transmission configuration provides spatial information for both (effective) infrared absorption coefficient and thermal diffusivity of semiconductor crystals. Moreover, the possibility of using lock-in thermography and photothermal radiometry microscopy in investigation of large area and thin films is discussed. [ABSTRACT FROM AUTHOR]

This study reports on a novel vacuum epitaxial lift-off (VELO) process to reuse the GaAs substrates in light-emitting diode (LED) production. The method is based on an epitaxial lift-off technique, whose application is however limited to flexible wafers, as gaseous reaction products (e.g. AsH 3 ) formed during the etching of AlAs with hydrofluoric acid are trapped within the wafer stack. In the developed VELO process, an applied vacuum of ∼ 5000 Pa to the bonded wafer stack removes such detrimental reaction gases, allowing a separation of hard substrate/carrier systems. The VELO process is evaluated with a state-of-the-art thin-film light-emitting diode (TF-LED) phosphide-based epitaxial structure with a buried AlAs sacrificial layer and a simplified LED chip construction at 4-in. wafer level. Characterization of the so-processed LEDs using high-resolution x-ray diffraction, μ -photoluminescence and electrical testing reveal that the VELO TF-LEDs show a comparable performance like to released chips by using conventional grinding/polishing and etching of the GaAs substrate. As our VELO process is non-destructive to the substrate, the GaAs wafers can be reused, enabling lower costs for LED production and reduced toxic waste to establish a green semiconductor production. [ABSTRACT FROM AUTHOR]

The structural and electronic properties of the bulk GaAs and Ge semiconductor and the band offsets for the GaAs/Ge and AsGa-Ge interfaces are investigated by density functional theory (DFT). This calculation has shown that the lattice parameter is underestimated by the local density (LDA) approximation and overestimated by the generalized gradient approximation (GGA). An opposite behavior is observed for the bulk modulus B 0 . Concern, the super-lattice GaAs/Ge (001), studied in our work, we found that the substitution of the atom of the interface affects the discontinuity of the VBO valence band, which is mainly due to the different electronic charges accumulated in the interfaces. [ABSTRACT FROM AUTHOR]

The deposition of InGaAs with an indium content of 0.3-0.5 and an average thickness of 3-27 single layers on a GaAs wafer by metalorganic chemical vapor deposition (MOCVD) at low temperatures results in the appearance of thickness and composition modulations in the layers being formed. Such structures can be considered to be intermediate nanostructures between ideal quantum wells and quantum dots. Depending on the average thickness and composition of the layers, the wavelength of the photoluminescence peak for the hybrid InGaAs quantum well-dots nanostructures varies from 950 to 1100 nm. The optimal average InGaAs thicknesses and compositions at which the emission wavelength is the longest with a high quantum efficiency retained are determined. [ABSTRACT FROM AUTHOR]

Triple-junction GaInP/GaAs/GaInNAs solar cells with conversion efficiency of ~29% at AM0 are demonstrated using a combination of molecular beam epitaxy (MBE) and metal-organic chemical vapor deposition (MOCVD) processes. The bottom junction made of GaInNAs was first grown on a GaAs substrate by MBE and then transferred to an MOCVD system for subsequent overgrowth of the two top junctions. The process produced repeatable cell characteristics and uniform efficiency pattern over 4-inch wafers. Combining the advantages offered by MBE and MOCVD opens a new perspective for fabrication of high-efficiency tandem solar cells with three or more junctions. Copyright © 2016 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Highlights: [•] Effects of environmental stresses (Unbiased HAST and HTS) on GaAs wafers are shown. [•] Different test structures were used to evaluate and interpret the results of the stresses. [•] This method allows a faster method for evaluating effects of process changes on device reliability. [•] Results of a process DOE evaluated by environment al stresses are presented. [ABSTRACT FROM AUTHOR]

Laser ablation of a gallium arsenide (GaAs) wafer immersed in distilled water was carried out using the fundamental wavelength of a high frequency Nd:YAG laser with 240 ns pulse duration. Rate of nanoparticles generation through laser ablation for various amounts of laser pulse energies (0.4–0.94 mJ) and repetition rates (400–2000 Hz) were studied and a maximum ablation rate of 19.6 µgr/s was obtained. Formation of the pure GaAs nanocrystals (NCs) is confirmed using TEM micrograph and X-ray diffraction analysis. Band-gap energy of generated GaAs NCs is calculated by Tauc method to be between 2.48 and 2.60 eV which is larger than the band-gap energy of bulk GaAs. The band-gap energy of NCs is increased by increasing the energy of laser pulses and is decreased by increasing the pulse repetition rate. [ABSTRACT FROM AUTHOR]