M. O. Manasreh

Photoreflectance and the electric fields in a GaAs depletion region

We present results which may resolve the recently reported discrepancy between the experimental and the calculated electric fields in the depletion region of undoped GaAs. The photoreflectance theory reportedly underestimates the electric field by nearly a factor of 2. We have found that changes in photoreflectance with laser pump penetration reveal the full character of the electric field over the entire depletion zone. It is often assumed that the built‐in surface potential produces a uniform electric field throughout a thin (100 nm) undoped layer of GaAs grown on top of a heavily doped energy pinning underlayer. Instead, it appears that the heavily doped underlayer provides a potential step at the interface. The step is separated from the surface depletion zone by a region of low electric field which is characteristic of the low fields found in thick, undoped GaAs with (2–4)×1014/cm3 of unintentional impurities.

Intersubband infrared absorption in a GaAs/Al0.3Ga0.7As quantum well structure

The linewidth, total integrated area, and peak position (ν0) of the intersubband transition (IT) in a GaAs/Al0.3Ga0.7As multiple quantum well, with doping in the barrier, are studied as a function of temperature using the infrared absorption technique. From the temperature dependence of the linewidth and the configuration coordinate model we find that the electrons in the GaAs well are weakly coupled to the GaAs normal optical phonon mode. The electron density (σ) in the quantum well is extracted from the total integrated area of the IT. From the temperature‐dependence of σ we conclude that the Fermi energy is also temperature dependent and that at 5 K it is about 36 meV above the ground state energy. We also find that ν0 increases as the temperature decreases. We calculated the absorption spectrum for the quantum well in a nonparabolic‐anisotropic envelope function approximation including temperature‐dependent effective masses, nonparabolicity, conduction‐band offsets, the Fermi level, and line shape bro...

Incorporation of carbon in heavily doped AlxGa1−xAs grown by metalorganic molecular beam epitaxy

Hole concentrations in excess of 1020 cm−3 have been achieved in AlxGa1−xAs using carbon doping during metalorganic molecular beam epitaxy. Hall and secondary‐ion mass spectrometry measurements show a 1:1 correspondence between the hole density and carbon concentration in as‐grown samples, although post‐growth annealing at 900u2009°C leads to a reduction in the net free‐carrier concentration (typically a decrease of ∼40% for 30 s anneals). The carbon‐localized vibrational modes (LVMs) show fine structure due to the presence of three different symmetries for substitutional carbon CAs, namely Td, C2v, and C3v. The experimental CAs LVM line positions are in remarkable agreement with the predictions of a rigid ion model.

Negative persistent photoconductivity in the Al0.6Ga0.4Sb/InAs quantum wells

We have measured the Shubnikov–de Haas (SdH) effect in the Al0.6Ga0.4Sb/InAs quantum wells under the negative persistent photoconductivity (NPPC) conductions. By illuminating the sample at low‐temperature, the carrier concentration of the two‐dimensional electron gas in the InAs well was reduced from 5.8 to 3.6×1011 cm−2 and the corresponding quantum lifetime increases from 0.16 to 0.21 ps. The electrons which escaped from the InAs well were captured by the ionized deep donors in the Al0.6Ga0.4Sb layers. The effective mass is equal to (0.0317±0.0005)m0. We also propose, based on the SdH data, that the illumination of the sample with the ionized deep donors at low temperature will exhibit the NPPC effect.

Additional H-related local vibrational modes in proton-implanted InP

At least 15 different hydrogen-related local vibrational modes (LVMs) are now found in proton-implanted InP as compared with the four we have previously reported. The additional LVMs are all observed by IR absorption in the 2200 to 2300 cm-1 region, are weaker in intensity than the original four, and are very reproducible in InP material from a variety of sources. Isochronal annealing studies indicate that some of these LVMs disappear by 250 degrees C but are then replaced by new LVMs, most of which are gone by 350 degrees C. These annealing characteristics are very different from the previously shown (four strongest) LVMs. All of these weaker LVMs are believed to be due to various P-H-related defect complexes.

Infrared absorption of electron irradiation induced deep defects in semi‐insulating GaAs

Electron irradiation induced defects in semi‐insulating GaAs grown by the liquid‐encapsulated Czochralski technique were studied using infrared absorption spectroscopy. A broad peak (P1) and a shoulder (P2) were observed in the infrared absorption spectra of the irradiated materials at 0.98 and 0.78 eV, respectively. The electron‐phonon coupling strength as well as the Franck–Condon shift of P1 was estimated from the temperature dependence of the linewidth. The annealing kinetics between 375 and 450u2009°C show that the P1 defect vanishes by a long‐range migration process with an enthalpy of 0.78±0.02 eV. A speculation for the atomic structure of P1 is presented.

Observation of the second energy level of the EL2 defect in GaAs by the infrared absorption technique

The second energy level of the EL2 defect (EL2+/++ ) is observed by using the infrared absorption technique and monochromatic light irradiation in undoped and lightly alloyed unannealed bulk GaAs. The EL2+/++ spectrum exhibits a complex structure and it does not exist in annealed samples. The EL2+/++ →EL20/+ and EL20/+ →EL2+/++ transitions were obtained by illuminating the samples with 0.7≤hν≤0.95 eV and 1.3≤hν≤1.5 eV, respectively. The transformation EL2+/++ ↔EL20/+ can be achieved in less than 10 s and can be repeatedly switched back and forth between the two states.

Temperature dependence of the photoinduced EL2*→EL20 recovery process observed by infrared absorption

The infrared absorption technique is used to measure the photoinduced recovery of the EL2 defect from its metastable state (EL2*) to its normal state (EL20) in semi‐insulating GaAs. This recovery is induced by irradiating photoquenched samples with 0.90 or 1.46 eV light for 60 min at various temperatures between 10 and 110 K. The recovery process is found to be highly temperature and sample dependent. It is concluded that the results are related to the presence of other defects and impurities (traps) which interact with EL2 at low temperatures.

Electron paramagnetic resonance study of the two‐dimensional electron gas in Ga1−xAlxSb/InAs single quantum wells

The Shubnikov–de Haas oscillations of the two‐dimensional electron gas in semimetallic undoped Ga1−xAlxSb/InAs single quantum wells with compositions x=0.1,0.2,0.5,0.8,1.0 are studied by X‐band electron paramagnetic resonance spectroscopy in the 4–20 K temperature range. The thermal equilibrium carrier concentrations vary from 4×1011 cm−2 for x=0.2 to 1×1012 cm−2 for x=1.0; from the temperature dependence of the Shubnikov–de Haas oscillations amplitudes in the 1–2 T magnetic field range the effective mass is determined to 0.026m0. Photoexcitation, with a low‐energy threshold of 0.7 eV, gives rise to a negative persistent photoconductivity (NPPC) for alloy compositions x≥0.2; no NPPC is observed for x=0.1.

Incorporation of Silicon and Aluminum in Low-Temperature Molecular-Beam Epitaxial GaAs

The localized vibrational modes (LVMs) of silicon donor (SiGa) and aluminum isovalent (AlGa) impurities in molecular beam epitaxial GaAs layers grown at various temperatures are studied using the infrared absorption technique. It is found that the total integrated absorption of these impurities LVMs is decreased as the growth temperature decreases. This finding suggests a nonsubstitutional incorporation of Si and Al in GaAs layers grown at 200u2009°C. On the other hand, a subtitutional incorporation is obtained in GaAs layers grown at temperatures higher than 350u2009°C. A recovery of the SiGa LVMs in GaAs layers grown at 200u2009°C has not been achieved by thermal annealing.