Photoreflectance spectroscopy (PR) is used to make in-situ diagnostics of subsurface damage behavior during Ar-plasma etching of n-type GaAs. The diagnostics in-situ PR first unveil anomalous damage behavior at an early stage of plasma etch- ing: Franz-Kerdysh oscillation shows an abrupt decrease in the surface electric-field strength from 130 to 30 kV/cm within 10 sec. This indicates that acceptor-like defects with a concentration of more than 1 × 1017cm−3 are created at the very beginning of the plasma etching. The δR/R abruptly decreased to 4% in intensity upon within 5 sec. of plasma etching and subsequently recovered. This indicates that recombination centers are quickly introduced, then further plasma etching gradually removes such centers, possibly by etching the damaged layer. Photoluminescence (PL) intensity decreases to 72% but does not show any recovery, indicating that PL is dominated by recombination centers in a deeper region. Thus, in-situ PR diagnostics is the first method to provide detailed findings on new damage behavior during Ar-lasma etching.

Reactive ion etching (RIE) of p-type 2-3 †cm resistivity silicon (100) was characterised using Photoreflectance (PR), Rutherford Backscattering Spectrometry (RBS) and Spectroscopic Ellipsometry (SE). Isochronal (5 minutes) etching was performed at various DC etch biases (0-500V) using a SiCl4 etch chemistry. The substrate etch rate dependence on applied bias was determined using mechanical profilometry. A distinct shift in the A3–A1 Si transition and significant spectral broadening of the room temperature PR spectra was observed as a function of etch bias. Photoreflectance results are correlated with RBS, SE and etch rate analysis. It is demonstrated that the PR spectra reflect a complex, competitive, plasma-surface interaction during the RIE process.

We have investigated IR reflectance spectra of semiconductor structures consisting of up to 5 epitaxial GaAs/GaAlAs layers on GaAs wafer, diffused and implanted profiles in Si wafers to find the semiconductor structures parameters.

High resolution electron beam lithography and reactive ion etching in methane-hydrogen (CH4/H2) plasmas have been used to fabricate InGaAs/InP open quantum well wires (QWW) with widths ranging from 200 to 40 nm and quantum dots (QD) with diameters ranging from 600 to 100 nm. Low temperature photoluminescence (PL) spectra were investigated in these nanostructures as a function of excitation intensity, wire width, and dot diameter. The peak emission of the dry-etched 40 nm wires is shifted to higher energies by about 2 meV as compared to 100 nm wires. This “open wire” result is consistent with results reported for buried InGaAs/InP wires of the same width. The blue-shift of the PL peak reaches 10 meV in QDs as their diameters decrease to 100 nm. The magnitude of the observed blue shift in the QDs is larger than the blue-shift predicted on the basis of quantum confinement for the same size dots.

Using contactless photoreflectance at 300K and 77K we have investigated the intersubband transitions from two modulation-doped GaAs/GaAlAs quantum dot (QD) arrays fabricated by reactive-ion etching (RIE). The samples consisted of 8 nm decoupled GaAs/GaAlAs quantum wells with dot sizes (lateral dimensions) of 60 and 100 nm. The lineshapes of the “IC-IH” and “IC-IL” features were indicative of a screened exciton, i.e., the derivative of a broadened twodimensional density of states (step function), due to the presence of the electron gas. On the other hand, even at 300K the “2C-2H“ features exhibited a well-defined sharp excitonic lineshape, i.e., derivative of a Gaussian profile. Even at room temperature it is possible to detect the effects of the lateral quantum confinement. We have observed a 2 meV blue shift of the “2C-2H” feature of the 60 nm QD array in relation to the 100 nm QD array. At 77K we have found evidence for a “parabolic-like” in-plane confining potential on the smaller QD array. This experiment demonstrates the considerable utility of PR in studying these reduced dimensional systems.

Raman and photoluminescence (PL) spectra have been used to characterize A10.3Ga0.7As/GaAs multiple quantum well (MQW) structures that have been patterned by focused ion beam (FIB) implantation followed by rapid thermal annealing (RTA). Microprobe Raman scattering is used to identify the appropriate RTA and FIB implantation conditions that provide for removal of implantation-induced damage and for compositional intermixing. FIB patterned wire-like structures are characterized by spatially resolved PL spectra.

Using Photoreflectance (PR) measurements, we have investigated In0.53Ga0.47As single quantum wells (SQW) with In0.52Al0.48As barriers grown by MBE on InP substrates. Unusual lineshapes of PR spectra are observed for the fundamental transition in some of the SQW. This phenomenon is shown to be independent on the widths of both the SQW (5nm or 10nm) and the surface barrier layer (between 65nm and 300nm). PR spectra are recorded at different temperatures and in different samples, as well as with a secondary pump laser beam. From these measurements, it is concluded that interface defects exist in the SQW grown at 525°C without growth interruption. Such defects are clearly evidenced in room temperature PR experiments and confirmed by PL measurements.

Phototransmittance has been used to investigate several pseudomorphic Al0.32Ga0.68As/In0.15Ga0.85As/GaAs high electron mobility transistor structures, with different values of the electron density ns. A lineshape analysis of the ground state transition made it possible to estimate ns, at room temperature. A signal from the Fermi-edge singularity (a manybody effect), was observed at low temperatures and the dependence of its intensity on temperature and electron density was examined.

InP-based lattice matched high electron mobility transistor (HEMT) structures have been characterized by liquid nitrogen temperature photoluminescence. A phenomenological line shape model has been utilized to fit photoluminescence spectra in order to obtain key parameters, such as the subband energies and transition amplitudes. From transition amplitude ratios and subband energies, fundamental quantum well characteristics are inferred. Changes in these parameters are linked to variations in the growth conditions of the epitaxial layer structures.

We report the results of a photoreflectance (PR) study of InGaAs/GaAs strained-layer quantum wells and superlattices (SLSs) grown by MBE on [111]B GaAs substrates. Under our measurement conditions, the PR spectra display features we can relate to the bandgaps of both materials and to optical transitions in the quantum structures. Using the photovoltaic effect to vary the surface electric field of our i-n+ and p+-i-n+ samples in a strictly contactless manner, we find optical transitions red-shifting with increasing intensity of illumination from a CW HeNe laser in [111]-grown structures, a well known effect which can be attributed to the straingenerated electric field (SGEF) present in these structures. We also find experimental support for the predicted effectiveness of free-carriers in screening the SGEF and thereby originating highly non-linear absorption.

We measured photoreflectance (PR) spectra at different temperatures between 80 and 300 K, and optical absorption (OA) at 3 K on MOVPE grown Inl-xGaxAs nearly lattice-matched to InP. x-ray diffraction measurements gave a lattice mismatch δa/ao = -0.9.10−3 between ternary alloy and InP, corresponding to × = 0.485. We obtained the energy gap dependence on T from PR spectra. The blue shift of the gap was accounted for in terms of compositional difference with respect to the perfectly lattice matched alloy (× = 0.472), and elastic strain; moreover PR and OA showed evidence of the valence bands splitting at k = 0 due to interfacial strain, in fine agreement with theory.

This paper demonstrates the utility of a Fourier transform (FT) Raman spectrophotometer in obtaining the room-temperature photoluminescence (PL) spectra of semiconductors used in photovoltaic and electro-optical devices. Sample types analyzed by FT-PL spectroscopy included bulk silicon and films of copper indium diselenide (CuInSej), gallium indium arsenide (GaInAs), indium phosphide arsenide, (InPAs), and gallium arsenide-germanium alloy (GaAsGe) on various substrates. The FTIR-PL technique exhibits advantages in speed, sensitivity, and freedom from stray light over conventional dispersive methods, and can be used in some cases to characterize complete semiconductor devices as well as component materials at room temperature. Recent innovations that improve the spectral range of the technique and eliminate instrumental spectral artifacts are described.

Fiber-based Fourier transform infrared spectroscopy for remote in-situ monitoring of organometallic delivery in organometallic chemical vapor deposition (OMCVD) is presented. The measurement is based on infrared absorbance of the organometallic reagent in a short single pass gas cell placed in the gas delivery line of an OMCVD system. The performance of the set-up is demonstrated for monitoring concentration transients during the delivery of two common OMCVD precursors, trimethylgallium (TMG) and trimethylindium (TMI). The time to reach saturation is shown to be faster for a TMG bubbler than for a TMI bubbler. This difference in delivery behavior is interpreted through a mathematical model of the gas handling lines and the monitoring gas cell. The utility of the system in monitoring temporal variations in TMI delivery is also demonstrated. Finally, the ability of the system to detect the chemical species unintentionally present in the feed lines is illustrated with the observation of methane gas from TMG and TMI bubblers that have been dormant for a period time. The methane gas is shown to quickly disappear with repeated used of the bubblers.

FTIR spectroscopy has been used to characterize as-deposited and chemical mechanical polished (CMP) electron cyclotron resonance (ECR) plasma based SiOx films. The ECR films were deposited at different O2/SiH4 gas ratios in an attempt to vary the film stochiometry. Transmission and reflectance-absorbance IR spectral data were combined with CMP removal rate information to characterize the SiOx films and their polishing behavior. The asymmetric O-Si-O stretching (ASM) and Si-OH vibrational bands were found to be principal sources of information.

Samples of chemically-vapor-deposited sub-micrometer-thick films of polysilicon were analyzed by transmission electron microscopy (TEM) in cross-section and by Raman spectroscopy with illumination at their surface. TEM and Raman spectroscopy both find varying amounts of polycrystalline and amorphous silicon in the wafers. Raman spectra obtained using blue, green and red excitation wavelengths to vary the Raman sampling depth are compared with TEM crosssections of these films. Some films have Raman spectra with a band near 497 cm−1, corresponding to numerous nanometer-scale faulted regions in the TEM micrographs.

The effect of ion-implantation followed by a rapid thermal annealing was investigated in borondoped silicon using photoluminescence (PL) spectroscopy. The radiation induced defects giving rise to the G, W and C PL lines are completely passivated by a hydrogen plasma treatment. However this hydrogen exposure also introduces broad and deep luminescence structure as well as new sharp PL lines very near the silicon band gap. Up to twelve new lines are observed at low temperature (< 20K). One of them exhibits a very low exciton localisation energy (≈ 2 meV) compared to the value measured for classical shallow donors or acceptors, and is observed only at very low temperature (≈4K). A broad deep PL band with a halfwidth of 30 meV is observed at around 925 meV. The excitation power dependence and the temperature dependence of the PL intensity of these sharp lines and the broad band are presented. Tentative correlations with the data currently available in the literature are presented for the understanding of the formation of the defects associated to the broad band as well as the sharp near band gap PL lines.

Raman scattering has been used to characterize ultrathin films of β-SiC, ranging in thickness from 38 nm to 240 nm. These films were prepared on the surface of a <100> Si substrate by a carbonization process at a temperature of 1300°C. In each case, the LO phonon near 970 cm−1 and the TO phonon near 795 cm−1 are observed, indicating the formation of β-SiC crystal. The Raman linewidths and peak positions indicate evidence of nonuniform stress and disorder. The Raman intensity of the TO phonon is nearly twice the intensity of the LO phonon measured both with and without the Si substrate, which indicates that the crystal growth was not entirely confined in the <100> direction.

Study of impurity-induced phonon disordering in Cdl-xZnxTe alloys is reported for a variety of samples by using far-infrared reflectivity and Raman scattering spectroscopy. Substantial differences were noted among the various published values for the optical phonon frequencies versus x. Contrary to an earlier Raman study on MBE grown Cdl-xZnxTe/GaAs films, our results within a twomode behavior, yield an increase of both the CdTe- and ZnTe-like transverse optical phonons with x. Unlike earlier speculations for a gap-mode in ZnTe : Cd of ∼140∼145 cm−1, our Greens function theory predicts it to be at a relatively higher frequency of ∼153 cm−1.

A 45 period GaAs/A10.54In0.46P superlattice was grown by molecular beam epitaxy using valved solid-sources to supply both the arsenic (As4) and the phosphorus (P2) group V fluxes. The room temperature optical transmission spectrum shows evidence of ground state excitons. Higher energy confined states are exhibited in photovoltage and photoreflectance spectra. Doublets corresponding to the m≈1 through m≈7 folded longitudinal-acoustic phonon modes are observed in the Raman spectrum. Analysis of these phonon doublets enables the structure of the superlattice to be determined. The interface roughness was found to be approximately 2 monolayers, and the layer thicknesses were determined to be 82 Å GaAs and 48 Å A10.54In0.46P.

The x-ray diffraction (XRD) of InGaAs/InP short-period superlattices (SPSL's) grown on (001)InP substrates by gas source molecular beam epitaxy (GSMBE) and by gas source migration enhanced epitaxy (GSMEE) shows that the GSMBE grown SPSL is strain free, and that GSMEE grown SPSL's with InGa-P and In-As heterointerfaces have strain-induced zerothorder satellite peak shift consistent with that in simulation results for the InGaAs/InP SPSL with one monolayer of InGaP and InAs inserted in each interface. Partial destruction of the long-range order is confirmed by the observation of the extra diffraction peak in GSMBE grown SPSL and by weak intensity of satellite peaks and nonuniform spacing between satellite peaks in GSMEE grown SPSL's. Raman scattering shows that the strain is accommodated in the interface layer in GSMEE grown samples. A confinement model without interface disorder fits the GaAs LO phonon very well. These results indicate that the local atomic arrangements are tailored by GSMEE, but that long range-order is impaired by the misfit dislocations in GSMEE grown SPSL's and by the exchange between As to P at the interfaces in GSMBE grown SPSL.