The small-pulse DLTS had been developed to measure distribution of deep levels in CVD grown SiGe/Si heterostructure before and after thermal processing at 800°C. Changes of defect states was found and after processing the original single deep level 0.62eV under the condition band split into two separated traps. A new weak deeper trap signal was found only in the just relaxed region. It could be Ge-related defect complex with misfit dislocations.

The 1.54μm emission of erbium implanted SiGe alloys was investigated as a function of oxygen and germanium concentrations as well as defect densities. Samples of SiGe layers grown by atmospheric pressure chemical vapor deposition technique which contain high concentrations of grown-in oxygen in the 10 19 - 1020 cm−3 range and 2 - 24 % Ge were chosen for the experiments. By using rapid thermal annealing in nitrogen atmosphere, a high optical activation of Er was found by photoluminescence. In samples with low defect densities nearly one third of the implanted Er ion dose could be detected in form of electrically active donors by spreading resistance measurements. The behavior of different SiGe : Er layers, based on sample property and annealing condition, suggests that more than only one type of luminescent Er-complex is present.

Amorphous silicon nitrogen alloy (a-Si:Nx) thin films have been deposited using a novel hot filament chemical vapor deposition (HFCVD) technique. In this method, a hot tungsten filament is used to decompose ammonia to obtain highly reactive nitrogen precursor species which further react with disilane to form silicon nitride thin films. This allows for very high deposition rates ranging from 600 Å/min to 2500 Å/min at low substrate temperatures. These films deposited at high rates show strong photoluminescence (PL) at room temperature in the visible region when excited with the 457 nm line of Ar+ ion laser. Intrinsic defects introduced into the amorphous silicon nitride matrix due to the rapid deposition rates seem to give rise to the visible PL. The PL intensity is at least 8-10 times stronger than silicon nitride films deposited by conventional plasma enhanced CVD. PL peak position of this broad luminescence was varied in the visible region by changing the film stoichiometry (Si/N ratio). The PL peak energy also scales predictably with the refractive index and optical band gap of the films. These samples showed reversible PL fatigue and also have band edge tail states characteristic of amorphous materials.

We investigate the effects of charged impurities in n-type Silicon inversion layers. We show the occurrence of ground and excited-state impurity bands as a function of electric field and concentration. Also the effects of disorder and for given impurity concentrations, the lowest excited band play an essential role in the optical and transport measurements. For high electric fields the impurity bands go to the ideally 2D separated bands.

We report preliminary results of a study of the activation volume for diffusion of arsenic in germanium. High-temperature high-pressure anneals were performed in a liquid argon pressure medium in a diamond anvil cell capable of reaching 5 GPa and 7500 C, which is externally heated for uniform and repeatable temperature profiles. The broadening of an ion-implanted arsenic profile was measured by Secondary Ion Mass Spectrometry. Hydrostatic pressure retards the diffusivity at 575°C, characterized by an activation volume that is +15% of the atomic volume of Ge. Implications for diffusion mechanisms are discussed.

Carbon has gained wide acceptance as a p-type dopant for GaAs-based device structures due to its low atomic diffusivity. Carbon doping of InGaAs, however, is complicated by the amphoteric nature of C and difficulty in incorporating C efficiently during epitaxial growth. We have achieved hole concentrations as high as 7x1019 cm−3 in CC14-doped InGaAs grown at low temperature by MOCVD. Growth-related issues include the effect of CCl4 on the alloy composition due to etching during growth, and the incorporation of hydrogen, which passivates the C acceptor and reduces the hole concentration during growth and during the post-growth cool-down. The effect of H passivation on minority carrier transport has been characterized by the zero-field time-of-flight technique. High frequency InP/InGaAs HBTs with a C-doped base have been demonstrated with ft = 62 GHz and fmax = 42 GHz, which is comparable to the best performance reported for MOCVD-grown InP/InGaAs HBTs.

Deep levels have been measured in molecular beam epitaxy grown Ga0.51In0.49P/GaAs heterostructure by double correlation deep level transient spectroscopy. Gold(Au) and Aluminum (Al) metals were used for Schottky contact. A contact-related hole trap with an activation energy of 0.50-0.75eV was observed at the A1/GaInP interface, but not at the Au/GaInP interface. To our knowledge, this contact-related trap has not been reported before. We attribute this trap to the oxygen contamination, or a vacancy-related defect, VIn or VGa. A new electron trap at 0.28eV was also observed in both Au- and Al-Schottky diodes. Its depth profile showed that it is a bulk trap in GaInP epilayer. The temperature dependent current-voltage characteristics (I-V-T) show a large interface recombination current at the GaInP surface due to the Al-contact. Concentration of the interface trap and the magnitude of recombination current are both reduced by a rapid thermal annealing at/or above 450°C after the aluminum deposition.

The development of novel optoelectronic devices using thick, defect free, strain free buffer layers mismatched to the substrate requires an understanding of the mechanisms responsible for the relaxation of the elastic strain. Using X-ray diffraction, we have studied the structural properties of partially relaxed InGaAs layers as a function of thickness and substrate misorientation and measured the residual strain. This study shows that strain free layers are difficult to achieve even for thicknesses well above the critical layer thickness. Our measurements also show that the relaxation of the strain induces geometrical effects such as a triclinic distortion of the epilayer unit cell and a tilt with respect to the substrate. These deviations from the ideal structure may seriously degrade the quality of optoelectronic active layers grown on relaxed lnGaAs buffer layers.

The defect distribution of a graded composition InGaAs layer grown on GaAs by MBE has been characterized by TEM (XTEM, PVTEM, HREM). The observed configuration does not correspond completely with that theoretically predicted. Dislocation misfit segments are in a quantity much bigger than in constant composition layers. Dislocation density is quite uniform up to a certain layer thickness t1. Few dislocations are observed between this t1 thickness and a larger thickness t2. Dislocation density is below the detection limit of XTEM for thicknesses bigger than t2. Some dislocations are observed to penetrate in the GaAs substrate.

Several mechanisms (reactions between 600 dislocations, Hagen-Strunk and modified Frank-Read processes) are proposed to explain the interactions of dislocations in the epilayer and their penetration in the substrate.

The Raman scattering from LO phonon–plasmon coupled (LOPC) mode in heavily carbon doped p–type InxGa1–xAs grown by metalorganic molecular beam epitaxy (MOMBE) was studied experimentally. Only one LOPC mode appears between the GaAs–like and InAs–like LO modes was observed. The peak position of the LOPC mode is near the GaAs–like TO mode frequency, and is not sensitive to the hole concentration. The intensity of the mode increases with increasing the carrier concentration while the two LO modes decrease and become unvisible under the higher doping level. The hole concentration dependence of the linewidth and intensity of the LOPC mode is very similar to that in p–type GaAs. It was shown that the plasmon damping effect plays a dominant role in the p–type doping case.

Deep levels in unintentionally doped A10. 48In0.52As layers epitaxially grown on InP substrates by low-pressure MOCVD have been investigated as a function of growth temperature (Tg ranging from 570 to 690°C). Two different origins for the residual carrier concentration are deduced depending on Tg: i) low growth temperatures favor the creation of a deep donor located at Ec-(0.13±0.04)eV; ii) At higher Tg, a preferential incorporation of a shallow donor occurs, which can be attributed to silicon by SIMS measurements. The oxygen contamination deduced by SIMS and the electrical characteristics of the AlInAs layers do not appear to be correlated.

GaAs and AlAs layers grown by CBE and doped with either 12C or 13C have been passivated with hydrogen or deuterium. Infrared absorption lines due to hydrogen stretch modes, symmetric A1 modes and “carbon-like” E modes of H-CAs and D-CAs pairs have been assigned for both isotopes in both hosts. Comparisons have been made with new ab initio local density functional theory and simple harmonic models. Anticrossing behaviour is found for the two types of coupled E modes in the two hosts. The dynamics of the H-CAs centre are very similar in GaAs and AlAs.

We report new methods to dope compound semiconductors. First, we demonstrate the concept of doping engineering whereby it becomes possible to tailor the activation energy of the dopant in a host semiconductor for the first time. In this application, the band offset of a thin, sacrificial semiconductor is used to lower the activation energy of the dopant below its value in the host semiconductor. This allows the freedom to control dopant activity in ways not accessible to a uniformly placed dopant. We chose δ-Be-AlGaAs/GaAs as a model example and show the hole binding energy is reduced by a factor of five. Secondly, we demonstrate overcoming the p-type solubility limit in GaAs by use of monolayer δ-Be in a GaAs base of an HBT. Here, an effective hole concentration of > 1021cm−3 is measured in real devices. We present a qualatative view of doping solubility limitations that are controlled by surface processes.

Carrier concentrations in doped InN, In0.37 Ga0.63 N and In0.75 Al0.25 N layers are reduced by both F+ ion implantation to produce resistive material for device isolation, and by exposure to a hydrogen plasma. In the former case, post-implant annealing at 450–500°C produces sheet resistances > 106 Ω/ℹ in initially n+ (7 x 1018 − 3 x 1019 cm−3) ternary layers and values of ∼5 x 103 Ω/ℹ in initially degenerately-doped (4 x 1020 cm−3) InN. The evolution of sheet resistance with post-implant annealing temperature is consistent with the introduction of deep acceptor states by the ion bombardment, and the subsequent removal of these states at temperatures −500°C where the initial carrier concentrations are restored. Hydrogenation of the nitrides at 200°C reduces the n-type doping levels by 1-2 orders of magnitude and suggests that unintentional carrier passivation occurring during cool down after epitaxial growth may play a role in determining the apparent doping efficiency in these materials.

Low temperature (2° K) photoluminescence (PL) measurements were performed for the wavelength (λ) region from 800 to 1600 nm on Be–doped GaAs grown by molecular beam epitaxy (MBE) for wide range of net hole concentration at room temperature (p) up to 2 x 1020 cm−3 after annealing at 850 °C for 20 minutes. The annealing procedure formed several new PL emission bands associated with deep levels appeared between 0.4 and 1.4 eV. The most intensive new PL band appeared at around 1.2 eV with a band width of about 0.2 eV for all samples investigated. Its peak position and band width were observed to shift slightly toward lower energy side and increase, respectively with increasing p. An additional two sharp bands appeared overlapping the main band at around 1.31 and 1.35 eV for p less than 1 x 1018 cm−3. New broad band formation was also observed at around 1.0 eV in the same samples. In addition, a new prominent PL band was found at about 1.35 eV in the as-grown samples with p = 5 ∼ 6 x 1017 cm−3, which disappeared entirely after annealing. The formation and annihilation mechanism of these deep levels after annealing can be presumably attributed to Be redistribution from Ga sites to As sites and interstitial sites to Ga or As sites, driven by the formation of As vacancies (V As) due to As evaporation from samples during annealing.

We have studied the IR absorption of heavily carbon doped GaAs grown by metalorganic molecular beam epitaxy. A striking observation is that the hydrogen-stretching vibration of a Crelated complex at 2688 cm−1 is strongly polarized along just one of the <110> directions in the (001) growth plane. This polarized C-H vibration is assigned to a defect complex that is aligned at the growth surface and then maintains its alignment as it is incorporated into the growing crystal. In a series of experiments, we have studied the annealing of the 2688 cm−1 band and its alignment and suggest that the defect complex consists of a CAs-CAs pair stabilized by hydrogen.

The effects of hydrogen plasma exposure upon electron Hall mobilities in InSb heteroepitaxial film grown on GaAs substrate have been investigated. After exposure to a hydrogen plasma at 250°C, the electron Hall mobility is significantly increased at low temperatures and the temperature dependence of the mobility is reduced. For the film with a broad x-ray rocking-curve width, 4 h-hydrogen plasma exposure can give rise to the enhancement of the mobility up to 6 times at low temperature. The mobility for the film with a narrow line width is enhanced around 1.5 times. These enhanced mobilities are nearly restored by 350°C rapid thermal annealing. The enhancement of the mobility due to hydrogenation is attributed to the satisfaction of the dangling bonds generated by the misfit dislocations.

Thermally stimulated depolarization current (TSDC) spectra are reported for AlxGa1-xAs alloys with direct and indirect bandgap for the first time. The experimental data reveal the presence of electric dipoles in both samples which are interpreted by using the negative-U DX center model. These data are fitted by a relaxation time distribution approach yielding average activation energies in close coincidence with the DX center binding energy value.

GaAs epilayers have been grown by Organo-Metallic Vapor Phase Epitaxy using dimethylaluminum methoxide as a dopant source. This compound contains a strong aluminumoxygen bond which is thought to remain intact during low temperature deposition and result in the incorporation of Al-O as a complex. Incorporation of aluminum and oxygen was investigated by Secondary Ion Mass Spectroscopy as a function of growth conditions: growth temperature, growth rate, V/III ratio, reactor pressure and dopant mole fraction. High doping levels up to 1020 cm−3 (for both oxygen and aluminum) were achieved without degradation of surface morphology andlor precipitation of a second phase. Oxygen concentration is lower than that of aluminum for all investigated growth conditions but at low deposition temperatures oxygen/aluminum ratios approach 1, indicating that Al-O is incorporated as a pair. Infrared absorption measurements in the 600-1200 cm−1 range did not detect well known isolated oxygen localized vibrational modes (LVM). Also in layers grown at low temperatures the intensity of isolated aluminum LVM at 362 cm−1 is much smaller than the concentration obtained by SIMS. Both observations prove that oxygen not only is incorporated as an Al-O pair but remains bonded in the bulk of the layer. Low temperature photoluminescence measurements indicate that the A1-O complex is electrically active in GaAs, forms a deep level within the GaAs band gap, and serves as an efficient non-radiative recombination center. Near band edge luminescence intensity correlates well incorporation of oxygen. The Al-O pairs act as deep acceptors in GaAs and cause the compensation of shallow tellurium donors.

Semi-insulating oxygen-doped GaAs layers have been grown by low pressure metalorganic vapor phase epitaxy (MOVPE) using aluminum-oxygen bonding based precursor diethyl aluminum ethoxide (DEALO). Resistivities of more than 2x109 Ω-cm at 294 K have been achieved. Deep level structure responsible for the high resistivity was investigated by deep level transient spectroscopy (DLTS) using DEALO and disilane co-doped GaAs p+-n homojunction. Multiple deep level peaks were observed, and the relative peak heights were found to vary with the dopant concentrations. Major deep levels were electron traps with ionization energy between 0.75 and 0.95 eV below conduction band edge minimum. An activation energy of 0.81 eV was deduced from temperature-dependent resistivity measurement, and should be closely related to the major0.75 eV peak in DLTS spectra.