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We have grown dilute InPN layers by liquid phase epitaxy and characterized them using high resolution x-ray diffraction, optical absorption, low temperature photoluminescence, and Hall measurement techniques. Our results indicate that a maximum amount of 0.2% nitrogen has been incorporated in the material with a band gap lowering consistent with expectations. The crystalline quality of the material is found to improve upon nitrogen incorporation. Large increase in luminescence from the material is observed after a high temperature annealing. [ABSTRACT FROM AUTHOR]

The evolution of InAs quantum dots grown on InP substrates by metal-organic vapor phase epitaxy is studied as a function of InAs coverage. Under specific growth conditions, the onset of the two- to three-dimensional transition proceeds via two distinct pathways: through (i) an abrupt appearance of quantum dots as expected in the usual Stranski-Krastanov growth picture and (ii) a continuous evolution of small surface features into well-developed quantum dots. The average size of the features in both these families increases with coverage, leading to a bimodal distribution in dot sizes at an intermediate stage of growth evolution. On further deposition of material, the two families merge into a single broad unimodal distribution of sizes. Complementary information obtained from independent measurements of photoluminescence spectra and surface morphology is correlated and is found to be independently consistent with the picture of growth proposed. [ABSTRACT FROM AUTHOR]

The growth of InAsxSb1-x/GaAs (x<=0.06) heterostructures has been achieved using liquid phase epitaxy. High resolution x-ray diffraction studies reveal that the films are single crystalline and structurally coherent with the substrate. It is also inferred from these measurements that the in-plane and out-of-plane strain arising out of mismatched epitaxy is almost completely relaxed, leading to a high dislocation density. The room temperature energy gap is measured to be 0.13 eV for InAs0.06Sb0.94/GaAs. Temperature dependence of the energy gap is studied between 93 and 433 K through the absorption spectra. Temperature dependent Hall and mobility measurements carried out between 10 and 370 K on these samples are discussed. [ABSTRACT FROM AUTHOR]

InGaAs strained quantum well (SQW) samples with lattice matched InGaAsP quaternary barriers are grown on GaAs substrates by metalorganic vapor phase epitaxy. These SQW samples are characterized using photoluminescence, photomodulated reflectance, surface photovoltage spectroscopy and high-resolution x-ray diffraction techniques. The results based on numerical calculations are used to identify the various transitions seen in the spectra. The effect of growth temperature on the indium content of the InGaAs SQW with lattice matched InGaAsP quaternary barriers is studied. Contrary to the reported higher value of indium incorporation in InGaAs SQW with GaAs (In-free) barriers when the growth is performed at low temperatures, we find that the indium content of the InGaAs SQW with InGaAsP (In-based) quaternary barriers decreases if the SQW is grown at lower growth temperatures. A possible explanation for this behavior is provided. © 2002 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Single crystal (100) wafers of n-InSb were implanted with 50 MeV Li3+ ions at various influences ranging from 10 to 10 ions/cm at room temperature. Investigations of the optical, electrical, and structural properties of the as-grown, irradiated, annealed wafers were carried out by infrared and Raman spectroscopies, Hall measurements, and high resolution x-ray diffraction (HRXRD). In the case of samples irradiated with an ion fluence of 1.610 ions/cm, electrical measurements at 80 K reveal that there is a decrease in carrier concentration from 8.510 (for unirradiated) to 1.1 10/cm and an increase in mobility from 5.4104 to 1.6710 cm/V s. The change in carrier concentration is attributed to the creation of electron trap centers induced by ion beam irradiation and the increase in mobility to the formation of electrical inactive complexes. Nevertheless, even with the irradiation at 1.610 ions/cm fluence the crystalline quality remains largely unaffected, as is seen from HRXRD and Raman studies. c 2001 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Presents information on a study which used positron annihilation spectroscopy in evaluating strain relaxation and some defects in metals, alloys and semiconductors. Experimental details; Results and discussion; Conclusions.

Presents information on a study which focused on the Ga-In-P based self-organized quantum dot like structures formed during growth of short period superlattices sandwiched between GaInP alloy layers grown on gallium arsenide substrates. Experimental details; Results and discussion; Conclusions.

We report the observation of oscillatory features (OFs) in the photoreflectance (PR) and contactless electroreflectance (CER) spectra of CdTe films grown on Si substrate, at energies below the band gap of CdTe. The simultaneous observation of OF in the reflectance (R) spectrum having the same period as those in the PR and CER spectra (as also their dependence on film thickness) provides a direct proof for optical interference effects as being the source of these features. However, in the present case the amplitude of the OF gets damped towards shorter wavelengths while remaining nearly wavelength independent in the longer wavelength region indicating a modulation mechanism different from those reported earlier. A series of experiments and simulations performed by us seem to indicate that while in PR the principal mechanism is the pump beam induced periodic temperature changes which in turn modulates the optical path length of the CdTe film, in CER the mechanism is the electric field induced modulation of the subband gap refractive index of the film through the electro-optic effect. The damping of the OF has been explained on the basis of subband gap absorption by the CdTe film. © 1997 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Deals with a study which examined the photoreflectance and photoluminescence spectroscopy of low-temperature gallium arsenide grown by molecular-beam epitaxy. Information on modulation-doped photodectector structures; Methodology of the study; Results and discussion.

Describes deep-level transient charge spectroscopy (QDLTS) of tin donors in Al[subx]G[sub1-x]As. Characteristics of the QDLTS; Advantages of the QDLTS technique; Factors which possibly contribute to band structure and configuration effects.

Presents a study that introduced an Urbach tail in the absorption spectra of In[sub0.72]Ga[sub0.28]As[sub0.60]P[sub0.40] by germanium (Ge) doping. Semilog plots of the absorption coefficient for samples containing increasing amounts of Ge; Features of the spectra; Types of disorders that produce band tailing.

Discusses the transport properties of high energy 120Sn implanted GaAs and the effect of annealing on the electrical properties of the implanted layer. Formation of two layers at depth of 8.7 and 11 micrometers from the surface of the substrate; Fabrication of Schottky diodes on the implanted substrates; Presence of high series resistance due to radiation defects.

Presents a study which demonstrated the usefulness of a low-frequency capacitance deep level transient spectroscopy technique for samples with resistance in series with the depletion capacitance. Effects of series resistance from the contact resistance of aluminum gallium arsenide epitaxial layers; Errors in the density and activation energy of traps; Advantages of the low frequency technique.

Observes the thermal degradation of indium-phosphorus in open tube processing. Experimental techniques; Details on the data analysis techniques; Conclusions.

Presents a study that examined the DX centers in tin-doped aluminum-gallium arsenide using deep-level admittance spectroscopy (DLAS). Methodology; Analysis of the capacitance and conductance of the samples; Evaluation of the DLAS activation energy plots of the samples.

Examines the temperature dependence of forward and reverse currents of a-Si:Ge:H-Pd alloy Schottky barriers. Diode quality factor; Current voltage measurements; Capacitance measurements.

Catering to a large undergraduate laboratory class requires the experiments to be robust, low maintenance, and easy to set up with low cost test equipment at the disposal of most university laboratories. Most introductory undergraduate semiconductor device laboratory courses utilize packaged semiconductor integrated circuit chips to illustrate the functioning and applications of fundamental semiconductor devices such as diodes and transistors. While such methods do justice to the illustration of device concepts, the packages abstract the device physics and manufacturing and promote a "black-box" mentality towards device engineering. We have proposed and implemented a novel undergraduate device laboratory experiment, where metal oxide semiconductor capacitor (MOSCAP) devices were designed and fabricated at our university cleanroom and provided to students to perform basic capacitance-voltage profile measurements. To allow over a hundred students to simultaneously perform the experiments, we fabricated miniature test jigs that served as probe stations with spring-loaded pogo pins to make electrical contact with the devices. Using a simple op-amp based circuit that is easy for second year undergraduates to analyze, students are able to successfully extract device parameters such as substrate doping density and flat-band voltage using this experiment, and visualize the different modes of operation of a MOSCAP. [ABSTRACT FROM AUTHOR]

Presents information on a study which determined the band offset of a strained-layer single quantum well by a capacitance-voltage technique. Methods; Results; Discussion.

Focuses on a study which examined the distinction of the absorption of a single quantum well from that of the substrate in a quantum well structure by using photothermal deflection spectroscopy (PDS). Description of the amplitude and the phase of the PDS signal of an indium phosphide substrate as a function of wavelength; Information on the subband gap region of the substrate; Absorption coefficient of the quantum well.

Discusses a study that presents evidences of the alloy broadening of the emission and capture rates of DX center. Frequency dependence of capacitance of Schottky barriers on aluminum gallium arsenic:silicon; Variation of the high-frequency capacitance as a function of temperature; Values of the fitting parameters used for the simulated c-f characteristics of the sample.

GaAs nanowires have been grown on single-crystal (001) Si and GaAs substrates using the vapour–liquid–solid (VLS) mechanism in a MOCVD chamber. These nanowires typically exhibited a circular cross-section with diameters in the range 10–40 nm. They contain a large density of growth twins that are here investigated in detail using transmission electron microscopy and high-resolution electron microscopy. Results indicate that the wires predominantly have the zinc blende diamond cubic structure with the growth axis parallel to &langle;111> and twins perpendicular to the growth axis. In many cases, multiple twins tend to cluster in groups along the length of the nanowires, either in a near-periodic fashion or on consecutive {111} planes, resulting in the formation of local regions exhibiting the hexagonal wurtzite structure of GaAs. The small difference in energy between these two forms of GaAs is likely to be the reason for the coexistence of both zinc blende and wurtzite structures within the same nanowire. [ABSTRACT FROM AUTHOR]

The effects of bombardment of 250 keV argon ions in n -type GaSb at fluences 2×10 15 and 5×10 15 ions cm -2 were investigated by high-resolution X-ray diffraction (HRXRD), Fourier transform infrared (FTIR) and scanning electron microscopy (SEM). HRXRD studies revealed the presence of radiation-damaged layer (strained) peak in addition to the substrate peak. The variation in the lattice constant indicates the strain in the bombarded region. The out-of-plane (ε &bot; ) and in-plane strains (ε | ) determined from the profiles of several symmetric and asymmetric Bragg reflections, respectively, were found to change with the ion fluence. Simulations of XRD patterns using dynamical theory of X-ray scattering (single-layer model) for the damaged layer yielded good fits to the recorded profiles. FTIR transmission studies showed that the optical density (α· d ) of GaSb bombarded with different fluences increases near the band edge with increase in ion fluence, indicating the increase in the defect concentration. The density of the defects in the samples bombarded with different fluences was in the range of 3.20×10 21 –3.80×10 21 cm -3 . The tailing energy estimated from the transmission spectra was found to change from 12.0 to 58.0 meV with increasing ion fluences, indicating the decrease of crystallinity at higher fluences. SEM micrographs showed the swelling of the bombarded surface of about 0.33 μm for the fluence of 2×10 15 ions cm -2 , which increased to 0.57 μm for the fluence of 5×10 15 ions cm -2 . [ABSTRACT FROM AUTHOR]

We describe two mechanical light chopper blade designs that can be used, with a monochromator and broadband light-source-based spectroscopy setup, to perform wavelength modulation spectroscopy. The left and the right half of a beam emerging from a monochromator would have spectral distributions that are skewed to longer and shorter wavelengths about the central wavelength for positive grating orders. Our two designs, the alternating double-slot blade and the vertical right-angled blade, allow switching between the two halves of the beam front to generate a small periodic variation in the wavelength distribution, enabling wavelength modulation spectroscopy. In contrast to existing methods of wavelength modulation, this technique does not require modification of the monochromator or the light source unit. We analyze the signal waveforms and show how, and under what conditions, wavelength modulation data can be extracted from the alternating signal components measured by the detector. To demonstrate their functioning and applicability, we have performed wavelength-modulated reflectance spectroscopy on epitaxial semiconductor samples using these chopper blades. [ABSTRACT FROM AUTHOR]

Measurements of electroreflectance and surface photovoltage spectroscopy of semiconductor structures are described using a transparent indium-tin-oxide-coated glass electrode in soft contact mode on the semiconductor surface. This improvisation (simplification) reduces the magnitude of the ac modulation voltage necessary for the electroreflectance measurement to less than a volt from about a kV (∼103 V) as required in the conventional contactless setup. This soft contact mode also enhances the sensitivity of the surface photovoltage signal by three orders of magnitude. We also formulate an analytical criterion to extract the transition energies of a quantum well from the surface photovoltage spectrum. © 2001 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Examines the use of photoreflectance spectroscopy with white light pump beam to characterize semiconductor heterostructures. Generation of excitation energy values by the pump beam; Reduction of signal strength in the dual chopping scheme; Determination of the luminescence intensity of the probe beam.