P. Y. Yu

Free carrier lifetime in semi‐insulating GaAs from time‐resolved band‐to‐band photoluminescence

Time‐resolved band‐to‐band photoluminescence offers a quick and contactless technique for determining the photoexcited free carrier lifetime in GaAs samples with deep traps.

Pressure dependence of Schottky barrier height at the Pt/GaAs interface

The Schottky barrier height at the Pt/GaAs interface has been measured as a function of pressure using a diamond anvil cell. The Schottky barrier height was found to shift to higher energy with a linear pressure coefficient of 11 meV/kbar, which is equal to the pressure coefficient of the fundamental gap of GaAs and with a nonlinear coefficient of −0.26 meV/kbar2. These results are discussed in terms of defect models which have been proposed to explain the Fermi level pinning in Schottky barriers.

BAND ALIGNMENTS IN GAINP/GAP/GAAS/GAP/GAINP QUANTUM WELLS

Pressure-dependent photoluminescence (PL) in several GaInP(ordered)-GaAs quantum well structures grown by metal organic vapor phase epitaxy is reported. Quantum well emission from GaAs is observed only in structures where thin (∼2 nm) GaP layers are inserted between the GaAs well and the GaInP barrier. By extrapolating the energies of the various inter and intralayer PL transitions observed under pressures (up to 5.5 GPa) to zero pressure, the different band offsets of the heterostructure have been determined.

Discovery of a new photoinduced electron trap state shallower than the DX center in Si doped AlxGa1−xAs

We have found a new electron trap state in Si‐doped AlxGa1−xAs by deep level transient spectroscopy and constant temperature capacitance transient measurements under strong light illumination. This new trap is shallower than the DX center associated with Si impurity in that its emission and capture activation energies are equal to 0.20±0.05 and 0.17±0.05 eV, respectively. Its maximum concentration is comparable to the concentration of the DX center. Possible origins of this new trap and its relationship to the DX center are discussed.

Laser-induced heating of nanocrystals embedded in glass matrices

Laser‐induced heating of nanocrystals embedded in silicate glass matrices has been studied by photoluminescence and Raman scattering. No nonequilibrium optical phonons were found both for cw and 150‐ps‐long laser pulses in contrast to bulk samples. The measured laser‐induced temperature rise in one sample where the nanocrystal radii are ∼5 nm was found to be in quantitative agreement with a nonlinear theory proposed by Lax for bulk semiconductors. However, in another sample where the nanocrystal radii are only 3 nm, the observed temperature rise at high laser powers was significantly higher than the theoretical prediction.

Properties of a CuAu phase of AgGaSe2 grown on [100] GaAs substrate

Recently, it has been suggested theoretically [A. Janotti and S.-H. Wei, Appl. Phys. Lett. 81, 3957 (2002)] that, if AgGaSe2 with the CuAu structure can be grown epitaxially on ZnSe, it will be an excellent source for spin-polarized electrons. Here we report the growth and properties of epitaxial films of AgGaSe2 with the CuAu structure on (100) GaAs substrates and compared them with those of chalcopyrite AgGaSe2.

OPTICAL STUDIES OF GAINP(ORDERED)/GAAS AND GAINP(ORDERED)/GAP/GAAS HETEROSTRUCTURES

We report on a detailed optical study of emission from a series of GaInP (ordered)/GaAs heterostructures. Some of these structures contain one or two thin (∼2 nm) layers of GaP between the GaInP and GaAs layers. A so-called “deep emission” band at 1.46 eV is observed in all our samples. However, at high excitation power, an emission above the band gap of GaAs (previously identified as quantum well emission) emerges only in structures where GaP layers are inserted on both sides in between the GaAs well and its GaInP barriers. From the pressure dependence we have identified the deep emission peak as due to donor–acceptor pair transitions at the GaAs/GaInP interface. The insertion of GaP layers between the GaInP (ordered) and GaAs layers helps to suppress the defects which contribute to this deep emission. By applying pressure to the sample which exhibits quantum well emission we have determined its band alignments. We show that the GaP layers form two effective barriers for confining electrons within the Ga...

Addendum: Deep emission band at GaInP/GaAs interface

We have performed high pressure photoluminescence studies of the deep emission band in GaInP/GaAs quantum well. Our results suggest that this peak is related to donor-acceptor pair transitions in the GaAs well.

Correlation between nanoscale and nanosecond resolved ferroelectric domain dynamics and local mechanical compliance

The local dynamics of ferroelectric domain polarization are uniquely investigated with sub-20-nm resolved maps of switching times, growth velocities, and growth directions. This is achieved by analyzing movies of hundreds of consecutive high speed piezo force microscopy images, which record domain switching dynamics through repeatedly alternating between high speed domain imaging and the application of 20-nanosecond voltage pulses. Recurrent switching patterns are revealed, and domain wall velocities for nascent domains are uniquely reported to be up to four times faster than for mature domains with radii greater than approximately 100 nm. Switching times, speeds, and directions are also shown to correlate with local mechanical compliance, with domains preferentially nucleating and growing in compliant sample regions while clearly shunting around locations with higher stiffness. This deterministic switching behavior strongly supports a defect-mediated energy landscape which controls polarization reversal,...

Measurement of the infrared transmission through a single doped GaAs quantum well in an external magnetic field: Evidence for polaron effects

Precise absolute far-infrared magnetotransmission experiments have been performed in magnetic fields up to 33 T on a series of single GaAs quantum wells doped at different levels. The transmission spectra have been simulated with a multilayer dielectric model. The imaginary part of the optical response function which reveals singular features related to the electron-phonon interactions has been extracted. In addition to the expected polaronic effects due to the longitudinal-optical phonon of GaAs, a kind of carrier-concentration-dependent interaction with interface phonons is observed. A simple physical model is used to try to quantify these interactions and explore their origin.