The piezoelectric photoacoustic (PPA) measurements before and after the secondary light illumination for 3 minutes were carried out at 85 K to investigate the electron and hole photoionization processes of EL2 in carbon concentration controlled semi-insulating (SI) GaAs. The result showed a broad peak around 1.0 eV and a hump up to the band gap energy. These were due to hole and electron photoionization processes of EL2, respectively, and these processes were clearly observed from a nonradiative recombination point of view for the first time. In addition, we found that the hole photoionization process of EL2 is not influenced by the secondary light illumination at low temperature. Although the electron photoionization underwent photoquenching effect upon an illumination of 1.12 eV, the hole photoionization process did not change even after a long period of illumination. The positively charged EL2 donor state may not transform to the metastable state.

The temperature dependence of the metastable transformation of EL2 is explained in terms of the thermal emission of holes from the actuator level, VA. A model including the thermal release of holes from this level is presented. The numerical solution allows to account for the low photoquenching efficiency above 80 K in an accurate way. The existence of this level was postulated on the bases of the electric compensation and the temperature dependence of the metastable transformation of EL2 in semiinsulating GaAs. This level allows a complete description of the driving mechanism of the metastable transformation of EL2.

It is found that interstitial agglomerates are formed uniformly in an irradiated area of InP by annealing at the temperature above 700 K after 200 keV-electron irradiation. TEM observation shows that the number density of interstitial atoms in the agglomerates reached a maximum value when the growth of all the agglomerates stopped. The final density did not depend on annealing temperature but on electron dose, and it increased quadratically with electron dose up to 2×1022 cm−2. In order to explain the experimental results, we have proposed a new model that the agglomerates are formed by thermal diffusion and agglomeration of interstitial-pairs, i.e. Ini-Pi interstitial-pairs. From the analysis, the migration energies for the pairs are estimated to be 1.52 eV. The onset temperature for the diffusion of the pairs is estimated as 550 K.

As the p-type dopant most often used in metalorganic chemical vapor deposition (MOCVD) of Group III - Group V compound semiconductors, Zn presents problems in device design and performance because of its high diffusivity in these materials. While Zn diffusion into n-type layers such as InP:S has been observed frequently, there is little known as to the electronic and optical properties of the resultant material. We have grown InP samples by MOCVD which are doped with both Zn and S to levels as high as 3×1018 cm−3. These samples were analyzed by electrochemical C-V profiling, van der Pauw-Hall analysis, secondary ion mass spectroscopy (SIMS), and low temperature (10K) photoluminescence spectroscopy (PL). We have determined that good hole mobility is maintained in InP:Zn samples that are simultaneously doped with S up to a level of 4×1017 cm−3. PL analysis of co-doped samples shows peaks between 0.91 and 0.92 μm which are indicative of donor-acceptor transitions, and broad peaks with energy levels of approximately 1.0 μm which may be indicative of ZnS complexes or precipitates. SIMS analysis of Zn diffusion into Fe doped substrates shows that Zn diffusion is reduced in the presence of S in the lattice.

We have investigated the effect of annealing on hydrogen-related donors in crystals of InP using Hall effect, infrared absorption, and photorefractive gain measurements. Hydrogen is believed to be incorporated during growth, forming a donor complex around an indium vacancy with hydrogen saturating all four dangling bonds. By observing the local vibrational mode of the hydrogen complex using infrared absorption at 2316 cm−1 was possible to observe a decrease in the concentration of the hydrogen defect after annealing. In the undoped crystal, the disappearance of this defect is accompanied by a decrease in the free carrier concentration as measured by Hall effect. These changes are correlated with a decrease in the absorption due to Fe2+ centers, which form when donors are compensated by the neutral acceptor Fe3+. The existence of the hydrogen-related donor complex is further substantiated by photorefractive experiments using 1064nm irradiation on the iron doped samples. All of the measurements point to the role of hydrogen as a contributor to the net shallow donor concentration in InP crystals.

We present investigations on the two dominating acceptor levels observed in Cu-diffused GaAs which have frequently been attributed to the two ionization levels of a double CuGa acceptor. We employed plasma hydrogenation and lithium diffusion followed by reverse-bias and zero-bias annealing to passivate and subsequently reactivate the Cu-related acceptor levels. Deep-level current-transient spectroscopy measurements reveal that the two levels are independently reactivated, strongly indicating that they arise from different defects.

The spectral and the time dependent piezoelectric photoacoustic (PPA) measurements under the continuous light illumination were carried out at 85 K to investigate nonradiative recombination processes involving EL2 defect levels in carbon doped semi-insulating (SI) GaAs. The decrease of the PPA signal due to the photoquenching effect of EL2 was observed for a short period of illumination of 1.12 eV. It was found that the photoquenching becomes drastic with increasing the carbon concentration. After fully photoquenching, the PPA signal increased again through a local minimum by the continuous light illumination and finally exceeded the initial value before illumination until the saturation level was reached. The deep donor level EL6 and its metastable state are proposed. EL6 level donates electrons to compensate a part of carbon acceptors after photoquenching. The nonradiative recombination through this level generates the PPA signal. The usefulness of the PPA technique for studying the nonradiative transition through deep levels in semiconductor is suggested.

Tellurium donors in GaP have been ionized by phonon assisted tunneling in the electric field of pulsed far-infrared laser radiation. In response to the laser pulse a photoconductive signal has been detected with a fast component reproducing the laser pulse and a slow component which rises after the irradiation has ceased and finally exponentially decays with a strongly temperature dependent time constant in the range of microseconds to several milliseconds. This temporal structure of the signal is explained by a cascade capture mechanism and subsequent accumulation of carriers in a long-living shallow donor excited state, identified as valley-orbit split 1s(E) level of Te. The final step of recombination is achieved by radiative transitions, which is proved by the observation of far-infrared to mid-infrared up-conversion.

A model is presented for the filtering of threading dislocations in InxGa1−xAs/GaAs epitaxial single layers by accurate control of the layer thickness. The model developed differs from previous models since the InxGa1−xAs growth is restricted to less than ten times the Matthews and Blakeslee critical thickness (hc) where the asymmetry in the [110] and [110] dislocation densities is the greatest. Beyond this thickness it is shown that the removal or annihilation of threading dislocations (TDs) in the epilayer is more than offset by the introduction of new TDs from spiral and Frank-Read type sources. Results from strain sensitive etching with CrO3 aqueous solutions show that the TD density can be reduced by up to a factor of ten below that found in the substrate. Atomic force microscopy shows that these thin layers maintain a high level of surface quality with an absence of striations. Evidence is also shown that this type of defect etching is suitable for revealing large scale dislocation blocking in samples that have been grown significantly beyond 10hc.

We report on the low temperature growth of AlxGa1−xAs by conventional Organometallic Vapor Phase Epitaxy OMVPE for a substrate temperature of 500°C and V/III ratios extending to subunity. Optical, structural and electrical qualities are assessed with double crystal X-ray diffraction, Nomarski and atomic force microscopy, 1.6K and 300K photoluminescence, Rutherford backscattering and Hall measurements. Although our low temperature grown films are of good structural and optical quality, they exhibit high background p-doping (carbon) and high levels of hydrogen passivation. A method for extracting the carbon doping levels from lattice contraction measurements is suggested. The dependence of layer composition, free carrier concentration and hydrogen passivation on growth parameters are investigated. Moreover, the effects of post-growth annealing on free carrier concentration, lattice parameter and optical qualities are studied. The influence on the bandgap of bandtail states and compressive strain due to carbon are compared.

The deposition of GaAs by MBE at low temperatures results in a material of unique properties. However, up to now the control and understanding of the electrical and structural properties are unsatisfactory. To investigate the influence of growth parameters on the formation of point defects and electrical properties, the substrate temperature and the As/Ga flux ratio were systematically varied. In a well defined parameter range the lattice expansion was found to be dominated by the formation of As antisite defects. After annealing a high resistivity is obtained independent of the growth conditions. A strong influence of the growth temperature on the band conduction mechanism is observed, whereas a variation of the As/Ga flux ratio induces only slight changes of the temperature dependence of the conductivity.

We show that in contrast to Si donor and Be acceptor doping, isovalent In impurity doping enhances arsenic excess in the GaAs films grown by molecular beam epitaxy at low temperature. This effect is due to an increase in the concentration of arsenic antisite defects. Gallium vacancy related defects are detected only in the samples annealed at high temperature. Their concentration is found to be higher in the indium-free material than in the indium doped one

We have investigated polarization of photoluminescence from the VGaTeAs complexes in n-GaAs induced through resonant excitation by polarized light. Experimental data in temperature range from 77 to 240 K were described by classic one-dipole approximation within the model of the VGaTeAs complex subjected to the Jahn-Teller distortion in the ground and excited states. It is shown that depolarization of photoluminescence at temperatures over ∼ 120 K may be explained by concurrent action of i) thermal emission and back capture of holes bound to the complexes in the excited state and ii) reorientation of complex distortion during a life of this state. The model parameters have been estimated.

Antiphase boundaries in GaP crystals epitactically grown on Si (001) have been characterized using transmission electron microscopy. Convergent-beam electron diffraction was used to identify the antiphase-related grains. The antiphase boundaries were observed to adopt facets parallel to specific crystallographic orientations. Furthermore, stacking-fault-like contrast was observed along the interface suggesting that the domains may be offset from one another by a rigid-body lattice translation.

Electrically detected magnetic resonance (EDMR) has been used to study carrier recombination in GaAs/AlGaAs quantum well structures grown by molecular beam epitaxy. The spin dependent photoconductivity signals depend strongly on the electrical contact properties. Using silver paste contacts a narrow (18 G) resonance located at g = 2.001 is observed. It has been previously attributed to surface defects on GaAs. Using alloyed In-contacts other signals are detected. The dominant resonance observed at 9 GHz has an isotropic g-value of g = 1.99 with a halfwidth of 200 G and is therefore assigned to Cr4+. Other signals of considerably lower intensity are explained by the well known electron paramagnetic resonance (EPR) properties of the Gai-interstitial and the AsGa-antisite defects. EDMR performed at 34 GHz allows the experimental separation of the two sets of hyperfine lines.

The electrical degradation of AlInAs /GaInAs high electron mobility transistor (HEMT) due to the fluorine contamination is quantitatively explained through the comprehensive annealing experiments and bias-temperature tests. The thermal degradation rate is found to be mainly determined by the following electrochemical reaction of fluorine with donor species after the quite fast diffusion of fluorine into the AlInAs layer. It is also confirmed that the thermal degradation is stringently affected by the electric field resulting in the one-sided degradation near the anode. These findings are important knowledges to improve the reliability of AlInAs/GaInAs HEMT under the DC accelerated life test at high temperature.

We report on the electrical and structural characterization of sulfur (S) doped Ga0.73In0.27As layers, grown on SI (001) GaAs substrates by chemical beam epitaxy. The room temperature free electron concentration is 2×1017cm−3 while the corresponding value of mobility is 3400 cm2V−1 s−1. The epilayer is characterized by a deep trap, which could be attributed to the electrical activity of dislocations, with an activation energy of 0.59 eV and a capture cross section 6×10−15 cm2. TEM analysis shows that the GaInAs/GaAs interface is characterized by dislocation lines and loop-like configurations which could be attributed to climb movement by point defect absorption or emission. Annealing at 420°C (Ar ambient for 5 min) does not alter the carrier concentration (n) and mobility (μ) significantly. The invariance of n and μ, even though the temperature should be high enough to dissociate any Satomic hydrogen complexes, indicates that the number of hydrogen-S donor complexes in the as-grown material is small compared with the donor concentration. Finally, the effect of intentional atomic hydrogen diffusion is discussed.

The properties of chlorine atoms in crystalline GaAs, such as stable configurations, migration paths, charge-state effects, and interaction with dopant atoms are theoretically investigated. The calculations are based on the local density functional theory using first-principles pseudopotentials in a supercell geometry. We determine the stable charge state of an isolated Cl atom as a function of the Fermi energy. When the Fermi level is situated at the top of the valence band of GaAs, the Cl atom occupies preferentially the bond-center site of a Ga-As bond in the positive charge state. The Cl atom diffuses through the GaAs crystal via a path in the region of high electron density, with a fairly large energy barrier. When the Fermi level is at the bottom of the conduction band, the lowest-energy configuration of the Cl atom is the tetrahedral interstitial site in the negative charge state and the bond center site is very slightly higher in energy. In Si-doped GaAs, the C1 atom occupies the tetrahedral interstitial site with the substitutional Si donor atom as a nearest neighbor, forming a neutral Cl-Si complex. The Cl-Si complex is weak and easily dissociates into the isolated C1 and Si atoms in GaAs. A comparison will be made between the behavior of Cl and F atoms in GaAs.

In situ Zn-doped InP layers are grown by low pressure metalorganic chemical vapor deposition at 620°C. Hole concentration increases with dopant flow rate, but reaches a saturated hole concentration of approximately 1.5 × 1018/cm3. Differently from the Zn-diffused InP case, photoluminescence (PL) of the in situ Zn doped InP shows band edge peak, e/D-A peak and distant D-A peak up to the hole concentration of 7.6 × 1017/cm3. These results can be explained by less generation of interstitial Zn atoms during in situ doping. PL characteristics of the in situ Zn-doped InP at the saturated hole concentration is extensively studied to explain its compensation mechanism. Two new deep bands, presumably responsible for the hole saturation behavior, are observed for the first time.

The InyGa1−yAs/GaAs superlattice on InxGa1−x.As (x<y) buffer layer was grown by MOCVD. The well layer is under compressive strain and the barrier layer is under tensile strain. However, both layers do not exceed the calculated critical value based on the M−yAs interface was smoother than the InyGa1−yAs/GaAs interface; the Indium composition gradual region at the GaAs/InyGal1−yAs interface was narrower than that at the InyGa 1−yAs/GaAs interface; in InyGa1−yAs alloy layer, the Indium composition near the GaAs/InyGa1-yAs interface was higher than that near another interface. For the first time, we explained the composition profile in this kind of superlattice based on the indium segregation theory. A new strain relaxation model, in which the 30-degree and 90-degree shockley partial dislocations were taken into account under both tensile and compressive strains, was presented to explain the difference of the smoothness between the GaAs/InyGa1−yAs interface and the InyGa 1−yAs/GaAs interface.