GaAs Bulk Substrate Research Articles

Effect of probe pulse duration in picosecond ultrasonics

Picosecond ultrasonics is a powerful tool for nanoscale metrology, giving access to dimensions and mechanical, thermal, and optical properties of nanomaterials. By monitoring the temporal evolution of the interaction of light with coherent acoustic phonons, also known as Brillouin oscillations, phonon lifetime and optical absorption can be measured. However, the extraction of these quantities can be inaccurate due to the common assumption of the infinite coherence length of probe pulses. Here, we demonstrate the effect of probe pulse duration on picosecond ultrasonic measurements numerically and experimentally. We establish a model that shows how the probe coherence length affects the measured signal loss and how we can overcome this limitation and measure an upper limit of the acoustic attenuation factor. The model is verified experimentally on a GaAs bulk substrate by varying the probe pulse duration, showing a strong effect for sub-100 fs pulses. Finally, we applied to CH3NH3PbBr3, where we reveal a high acoustic attenuation factor, which is in line with recent claims of strong anharmonicity in halide perovskites.

Demonstration of Single Crystal GaAs Layers on CTE-Matched Substrates by the Smart Cut Technology

Templates made of a thin single crystal GaAs layer on CTE-matched substrate (sapphire) have been realized using the Smart CutTM technology. These templates can withstand high processing temperatures thanks to the CTE matching between the GaAs thin film and its support, and therefore can be used for many applications since they require no specific restriction concerning thermal treatments. The GaAs templates have been compared to conventional bulk GaAs substrates. TEM images and XRD spectra show similar crystalline quality. AFM measurements show a similar surface microroughness. Photoluminescence of a AlGaAs double heterostructure grown by MOCVD on the GaAs template shows the same intensity as a reference structure on bulk GaAs. Therefore, the GaAs templates can replace GaAs bulk substrates in various domains such as photonics devices (solar cell, laser) or high frequency electronics.

MOS capacitors with metal gate/high-k dielectrics on GaAs bulk substrate

This paper investigates the electrical characteristics at low temperatures through C–V, I–V and conductance measurements to understand the interface behavior of HfO2 and p-type GaAs bulk substrate. Room temperature interface state density, D it , estimated for as-deposited Ti–Au/HfO2/GaAs capacitors was found to be 3.68 × 1011 cm−2 eV−1. Low temperature measurement suggests that only fast interface states contribute to the conduction process. When the characteristics of two different metal gates were compared, the accumulation capacitance density observed to be 1.4 and 8.98 fF/μm2 for Be–Au/HfO2/GaAs and Ti–Au/HfO2/GaAs, respectively at 1 MHz.

Ballistic electron emission microscopy on spin valve structures

Spin valve structures, as employed in base layers of spin valve transistor devices, are characterized by ballistic electron emission microscopy (BEEM). In detail, Co–Cu–Permalloy–Au layers sputtered onto n-type GaAs bulk substrates were studied. BEEM spectra taken on these multilayers show that magnetocurrents on the order of 600% can be achieved even at room temperature. Small area images (400nm×400nm) show that the spin filtering effect of the spin valves is quite homogeneous on the submicron scale. On larger scales, magnetic domains were imaged close to the switching field of the spin valve structure.

Onset of plasticity in a Σ = 5 GaAs compliant structure

Compliant structures have been fabricated in which a thin GaAs layer (thickness between 10 and 20nm) was bonded on top of a GaAs substrate with a large twist angle (about 37). This twist angle value was chosen so that the energy of the boundary (coincident boundary of type =5 (001)) was minimized. The structure of the interface was characterized and the onset of plasticity in such a compliant substructure was investigated using nanoindentation that allowed the low-load deformation regime to be observed. The results are compared with those obtained under the same conditions on a GaAs bulk substrate alone. No plastic zone was observed by transmission electron microscopy in the compliant structure under loads below 0.25mN while, under the same loads, plastic deformation was observed in the bulk substrate. For higher loads (2mN), plastic-flow enhancement was observed in the compliant structure. The results are discussed in the light of the arrangement of dislocations observed in the plastic zones.

Growth of InGaAs multi-quantum wells at 1.3 μm wavelength on GaAs compliant substrates

InGaAs multiple quantum wells at 1.3 μm wavelength have been grown on a twist-bonded GaAs compliant substrate. The GaAs compliant substrate contains a 30 Å GaAs thin layer bonded to a GaAs bulk substrate with a 22-degree angle. Nomarski phase contrast microscopy, transmission electron microscopy (TEM), and photoluminescence were used to characterize the heteroepitaxial layers. The smooth and crosshatch-free surface morphology, dislocation-free cross-sectional TEM, and strong luminescence intensity all provide convincing evidences for substantial improvement of the quality of heteroepitaxial material using the compliant substrate technique. Research is underway to apply the concept and technique of compliant substrate to Si and other materials.

Lattice engineered compliant substrate for defect-free heteroepitaxial growth

Presented here is proof-of-principle that a thin single crystal semiconductor film—when twist-wafer bonded to a bulk single crystal substrate (of the same material)—will comply to the lattice constant of a different single crystal semiconductor thick film grown on its surface. In our experiment, a 100 Å film of GaAs was wafer bonded to a GaAs bulk substrate, with a large twist angle between their 〈110〉 directions. The resultant twist boundary ensures high flexibility in the thin film. Dislocation-free films of In0.35Ga0.65P(∼1% strain) were grown with thicknesses of 3000 Å, thirty times the Matthews–Blakeslee critical thickness, on twist-wafer-bonded films of GaAs.

Optically pumped [formula omitted] lasers on [formula omitted] substrates

Optically pumped lasing has been observed up to 100 K in a Cd 0.2Zn 0.8Te ZnTe superlattice grown on a GaAs Si substrate. At 100 K, rapid degradation of the lasing signal is seen. This result is inferior to that previously reported for a similar structure grown on a GaAs bulk substrate, for which room-temperature lasing was seen with no degradation. X-ray rocking curve and morphology measurements suggest that the II–VI epilayer has limited ability to heal the extra defects that are present when a GaAs Si , rather than a bulk GaAs, substrate is used.

Electrical Damage Due to Low Energy Plasma Processing of GaAs Structures

ABSTRACTThe effect of numerous plasma reative ion etch and physical milling processes on the electrical behavior of GaAs bulk substrates has been investigated by means of electric microwave absorption. It was seen that plasma treatments at quite low energies may significantly affect the electrical quality of the etched semiconductor. Predominantly physical plasma etchants (Ar) were seen to create significant damage at very low energies. Chemical processes (involving Cl or F), while somewhat less pernicious, also gave rise to electrical substrate damage, the effect greater for hydrogenic ambients. Whereas rapid thermal anneal treatments tend to worsen the electrical integrity, some substrates respond positively to long-time high temperature anneal steps.

Photoluminescence determination of the nonuniformity of Fe, Zn, and other centers in undoped semi-insulating liquid-encapsulated Czochralski GaAs

2-K photoluminescence was used to determine the amount of nonuniformity present in undoped semi-insulating GaAs bulk substrate materials grown by the liquid-encapsulated Czochralski method. The relative photoluminescence intensities of the intracenter (5T2−5E) transition of the Fe2+ state, the near-band-edge transitions, and the Zn peaks, measured across the wafer diameter, show almost the same ‘‘W’’ pattern. The deep-center bands at 0.63 and 0.77 eV were also measured. Possible mechanisms of the photoluminescence intensity variation are discussed. In the materials used, a predominant shallow acceptor was observed to be Zn.