Strain-induced Piezoelectric Polarization Research Articles

Piezoelectric effects in ultrahigh quality AlGaAs/GaAs single quantum wire

Optical properties of V-shaped AlGaAs/GaAs single quantum wire with improved interface quality are investigated by means of photoluminescence (PL), PL excitation (PLE), and time-resolved PL measurements. Zero PLE absorption intensities are observed at low temperatures around ground state transitions. Excitation power density-dependent optical properties provide evidence that the zero PLE absorption intensities are due to an internal electric field created by the tiny strain-induced piezoelectric polarization along the wires, which causes complete spatial separation of the electron and hole wavefunctions along the wires.

Effect of Well Thickness on GaN/AlGaN Separate Confinement Heterostructure Emission

We investigated the effects of well thickness on spontaneous and stimulated emission (SE) in GaN/AlGaN separate confinement heterostructures (SCHs), grown by low pressure metal organic chemical vapor deposition. The SCH wells are unstrained and lattice matched to a GaN buffer layer. Our series of SCHs had GaN well thicknesses of 3, 5, 9, and 15 nm. We explain the spontaneous emission peak energy positions of the SCHs in terms of spontaneous and strain-induced piezoelectric polarizations. At 10 K, the carrier lifetime was found to be lowest for a 3 nm well, and the SE threshold was lowest for a 5 nm well. We show that the screening of the piezoelectric field and the electron-hole separation are strongly dependent on the well thickness and have a profound effect on the optical properties of the GaN/AlGaN SCHs. The implications of this study on the development of near- and deep-ultraviolet light emitters are discussed.

Effect of Well Thickness on GaN/AlGaN Separate Confinement Heterostructure Emission

We investigated the effects of well thickness on spontaneous and stimulated emission (SE) in GaN/AlGaN separate confinement heterostructures (SCHs), grown by low pressure metal organic chemical vapor deposition. The SCH wells are unstrained and lattice matched to a GaN buffer layer. Our series of SCHs had GaN well thicknesses of 3, 5, 9, and 15 nm. We explain the spontaneous emission peak energy positions of the SCHs in terms of spontaneous and strain-induced piezoelectric polarizations. At 10 K, the carrier lifetime was found to be lowest for a 3 nm well, and the SE threshold was lowest for a 5 nm well. We show that the screening of the piezoelectric field and the electron–hole separation are strongly dependent on the well thickness and have a profound effect on the optical properties of the GaN/AlGaN SCHs. The implications of this study on the development of near- and deep-ultraviolet light emitters are discussed.

Well-thickness dependence of emission from GaN/AlGaN separate confinement heterostructures

We investigated the effects of well thickness on spontaneous and stimulated emission (SE) in GaN/AlGaN separate confinement heterostructures (SCHs), grown by low-pressure metalorganic chemical vapor deposition. The SCH wells are unstrained and lattice-matched to a GaN buffer layer. Our series of SCHs had GaN well thicknesses of 3, 5, 9, and 15 nm. We explain the spontaneous emission peak energy positions of the SCHs in terms of spontaneous and strain-induced piezoelectric polarizations. At 10 K, the carrier lifetime was found to be lowest for a 3 nm well, and the SE threshold was lowest for a 5 nm well. We show that the screening of the piezoelectric field and the electron-hole separation are strongly dependent on the well thickness and have a profound effect on the optical properties of the GaN/AlGaN SCHs. The implications of this study on the development of near- and deep-ultraviolet light emitters are discussed.

Evidence for relaxed and high-quality growth of GaN on SiC(0001)

By using polarization-dependent x-ray absorption spectroscopy at the Ga edge, we study the growth of GaN on SiC(0001) in the thickness range 0.7–150 nm. We find that the growth is always relaxed (i.e., nonpseudomorphic) even for the thinnest epilayers, i.e., below the expected critical thickness. No evidence is found for a mixed Ga/Si interface plane, while a C/N mixed interface plane cannot be ruled out. The results are discussed with reference to the electronic structure of the SiC/GaN heterojunction and in particular to band offsets and strain-induced piezoelectric polarization.

Involvement of estrogen in the age-related decrease in cognitive performance of the senescence-accelerated mouse (SAM-P8)

Compared with conventional Ohmic-contact nanosensors, Schottky-contact has been introduced as a fundamentally new design for much enhanced sensitivity and improved responsive time of one-dimensional nanostructure based sensors. Here we demonstrate ZnO micro/nanowire sensors for hydrogen (H2) and nitrogen dioxide (NO2) detections at room-temperature based on a metal–semiconductor–metal (M–S–M) structure. By utilizing strain-induced piezoelectric polarization charges presented at the vicinity of local interface to modify the band structure at Schottky contact, piezotronic effect has been introduced to gate/modulate the charge carriers transport process across the M–S contact and thus hugely enhance/optimize the performances of H2/NO2 gas sensors. Upon straining, the detection sensitivity and resolution are obviously improved, together with a significant enhancement in output current by 5359% for H2 and 238.8% for NO2 detection. This work provides a promising approach to raise the sensitivity, improve the detection resolution, and generally enhance the performance of gas sensing, making it possible for fabricating room temperature of gas sensor while preserving its sensitivity.