The W/n-GaAs Schottky junctions A and B of area 1.75×l0-2 cm2 were fabricated by deposition of W on the chemically etched polished surfaces of n-GaAs samples by rf sputtering using a rf powers of 300 Watt for 30 min. The W contact B was subjected to a 90 min. thermal anneal at 390 °C. The room temperature I-V and C-V/f (with 200 Hz < f < 1 MHz) measurements were carried out for both the as-deposited and thermally annealed W/n-GaAs Schottky junctions A and B, respectively. From the direct I-V data, the values of 1.09 and 8.1×10-8 A for the ideality factor (n) and the reverse saturation current (Io), respectively, were estimated for the diode B, compared to the values of n=1.70 and Io=6.3×10-6 A for the diode A. The observed frequency dispersion in the zero bias capacitance in the diode B was attributed to fast interface states with a time constant, τ2=6 μs and density, Nss2=5.8×1010 eV-1cm-2, whereas, both the slow interface states (with τ1=4 ms and density, Nss1=7.8×1012 eV-1cm-2) and fast states (with τ2=1 μs and density Nss2=8.6×1010 eV-1cm-2) were responsible for the observed frequency variation of the zero bias capacitance in the diode A. For the forward bias values in the range 20-100 mV, the frequency dispersion in the measured capacitance suggested the presence of both the fast and slow interface states (with time constants differing by three orders of magnitude) in the as-deposited and the heat treated W/n-GaAs interfaces. Thermal anneal at 390 °C for 90 min. lowered the density of states at the W/n-GaAs interface by two orders of magnitude and resulted in the formation of a high quality rectifying W contact to n-GaAs with a rectification ratio of 1.4×104, a low Io and an ideality factor close to unity.

The relationship between electrical properties and microstructure of pure Zn and Au(Zn) contacts to p-GaAs has been studied. Thermally activated changes in ФB correlate with structural processes at MS interfaces. For Zn/GaAs contacts, lowering of ФB from 0.63 eV to 0.35 eV corresponds to the penetration of Zn into the native oxide layer. In AuZn/p-GaAs contacts, β-AuZn phase is responsible for the formation of ФB=0.4 eV in as-deposited contacts. The onset of the ohmic behaviour of Au(Zn)/p-GaAs contacts (ФB=0.3 eV) coincides with the appearance of α3-AuZn phase for Zn content less than 20 at.% or α1-AuZn, for higher Zn concentrations.

The obtained results prove that the mechanism responsible for the formation of low-resistance Zn -based contacts to p-type GaAs is associated with the lowering of the Schottky barrier at the metal/semiconductor interface. We suggest that the ultimate properties of these contacts are determined by the presence of a single, specific phase in a direct contact with the semiconductor.

Depositing Pd or Au on InP at substrate temperatures near 77K has previously been found to significantly reduce the interaction between the metal and semiconductor upon formation of the interface. In this work, this technique was used to fabricate metal-semiconductor-metal photodetectors (MSMPD’s) on semi-insulating (SI) InP substrates with superior characteristics compared to detectors formed using standard room temperature (RT) metal deposition. The low-temperature (LT) metallizations were patterned using a polyimide/SiO2 lift-off mask, and a SiO antireflection coating was used to attain near-zero reflection at λ=840nm. The detectors had an active area of 200μm × 200μm, and line widths and line spacings of 3μm. Detectors having a LT-Pd/SI-InP structure had a dark current of 80nA at 5V, which was a factor of 4 lower than the dark current of conventional MSMPD’s. Additionally, LT-Pd/SI-InP MSMPD’s exhibited excellent saturation characteristics and a responsivity of 0.75 A/W. Detectors with an indium-tin-oxide (ITO)/LT-Au(200Å)/SI-InP structure had a higher responsivity of 1.0 A/W, due to the relative transparency of this metallization. In contrast, MSMPD’s with RT metallizations had poor saturation characteristics, consistent with the results of others. The difference in the illuminated characteristics of MSMPD’s with RT and LT metallizations was due to a change in the internal photoconductive gain mechanism. In RT detectors, hole trapping at interface states near the cathode dominated the gain mechanism. In LT detectors, the difference in carrier transit-times dominated.

Experimental results of the internal quantum yield Yi associated with the internal photoemission on Au/n-Si structures are presented. The samples were prepared on Si(100) and Si(111) substrates with photoemitter layer thicknesses ranging from 5 nm to 50 nm. The Yi was measured at temperatures between 165 K and 300 K with the photoexciting energy varying from 0.72 eV to 1.07 eV. It was found that the Yi increases with decreasing Au layer thickness with a strong enhancement (40 times) in regard to the conventional Fowler theory. This experimental result is in good agreement with model calculations taking account of hot carrier scattering in the photoemitter layer. Barrier energies are larger than deduced from the Fowler plot.

Poly-Si TFT’s were fabricated on the glass substrate by the Metal Induced Lateral Crystallization(MILC). Before deposition of the active a-Si thin films(1000 Å), the glass substrate was pretreated in three different ways such as oxidation of a-Si(100 Å), oxide buffer layer deposition(1000 Å), and ion mass doping of the glass substrates. The leakage current at reverse bias could be reduced by one order of magnitude by the substrate pretreatment. Field effect mobility of n-channel TFT’s was 108cm2/Vsec, subthreshold slope and on/off current ratio were 0.7 V/dec. and about 106, respectively.

In this study the SCP (Surface Charge Profiling) method, based on non-contact, small-signal ac-SPV measurement is used to study thermal activation of boron in the near surface region of p-type Si wafers. Boron tends to form pairs with impurities such as hydrogen, iron and copper in the near surface region of Si substrates which render it inactive. During device processing, activation of boron may take place resulting in uncontrolled variations in active boron concentration in the near surface region.

In this work, both boron doped, polished CZ wafers and wafers with boron doped epitaxial layers are studied. In the former case, the concentration of active boron in the near surface region was initially up to an order of magnitude less than the bulk concentration determined from four-probe measurements, but increased with the temperature of an anneal in ambient air and approached the bulk value. In contrast, the wafers with epitaxial layers showed no consistent variations of surface dopant concentration with temperature. These results confirmed previous findings that the near surface region of the polished wafers is contaminated with metals introduced during polishing operations. The SCP method was found to be very effective in monitoring variations in active boron concentration in the near-surface region.

The reduction in the dimensions of advanced semiconductor devices has brought about the need for new metallization materials with low resistivity and high electromigration resistance. The Cu3Ge, has been suggested as a contact and metallization material due to its low resistivity (6 μΩ-cm), high electromigration resistance, and high chemical stability. We have grown thin films of Cu3Ge on (100) Si by the sequential e-beam deposition of an amorphous Ge layer then a Cu layer, followed by a thermal anneal to crystallize the Cu3Ge film. The Cu-Ge films maintain their low resistivity (10-15 μΩ cm) over a range of anneal temperatures, up to an anneal temperature of 600°C, where a significant increase in resistivity is observed. We have shown that this increase in resistivity is directly related to the structure of the Cu3Ge film and interface. We have observed by cross-sectional transmission electron microscopy (TEM), that films of Cu3Ge form a smooth, atomically sharp interface with (100) Si, up to an anneal temperature of 600°C, where the film agglomerates, and additional compounds are observed. In this paper, we discuss the correlation between microstructure, interface structure and electrical properties of these novel thin film structures.

In/n-In0.46Ga0.54P Schottky diode was fabricated by thermal evaporation of In on chemically etched surface of In0.45Ga0.54P:Si epitaxial layer grown on highly doped n type GaAs. The In metal formed a high quality rectifying contact to In0.46Ga0.54P:Si with a rectification ratio of 500. The direct current-voltage/temperature (I-V/T) characteristics were non-ideal with the values of the ideality factor (n) between 1.26-1.78 for 400>T>260 K. The forward I-V data strongly indicated that the current was controlled by the generation-recombination (GR) and thermionic emission (TE) mechanisms for temperature in the range 260-400 K. From the temperature variation of the TE reverse saturation current, the values of (0.75±0.05)V and the (4.5±0.5)×10-5 Acm-2K-2 for the zero bias zero temperature barrier height (φoo) and modified effective Richardson constant were obtained. The 1 MHz capacitance-voltage (C-V) data for 260 K < T < 400 K was analyzed in terms of the C-2-V relation including the effect of interface layer to obtain more realistic values of the barrier height (φbo). The temperature dependence of φbo was described the relation φbo =(0.86±10.03) - (8.4±0.7)×l0-4T. The values of φoo, obtained by the I-V and C-V techniques agreed well.

We have investigated experimentally and theoretically the elastic conversion tunneling of charge carriers in MOS structures Au on p+-InAs with superthin (10-20 Å) oxide film, the structures used in infrared photodetectors. In these structures the Schottky barrier provides near-surface inversion layer. The tunnel current-voltage (I-V) curves obtained at helium temperatures demonstrate the negative differential resistance region (NDR). We develop semiclassical two-band transfer matrix approach to the conversion tunneling analysis in a multilayer structure and calculate on its base the I-V curves dependence on the structure parameters. The NDR occurs to be caused by the motion of the remote quantum level in the inversion layer. The calculated I-V characteristics agree with the experimental ones quite well. The very existence of NDR and the shape of I-V curves depends strongly on the nature of localized electron states at the semiconductor interface. The characteristics of these electron states are used in the calculations as fitting parameters. Therefore, we suggest a new method for the interface states diagnosis.

Various optical techniques have been developed over the last few years to allow real-time analysis of regions of importance for semiconductor epitaxy, in particular the unreacted and reacted parts of the surface reaction layer (SRL) and the near-surface region of the sample. When coupled with emerging microscopic methods of calculating optical properties, these approaches will allow several levels of control beyond that which has been currently demonstrated.

Strained (x=0.48) and lattice-matched (x=0.53) InxGal-xAs/InAlAs/InP (100) MQWs have been investigated by photoreflectance. In the strained sample the relative intensities of the light-hole and heavy-hole excitonic transitions is different for the two different polarizations of the incident light parallel and perpendicular to the ]0-1-1 ] direction. This polarization anisotropy is explained in terms of the spontaneous formation of “quantum wires” and the presence of anisotropic strain due to spinodal-like phase decomposition of the InGaAs alloy in In-rich and Ga-rich regions.

Epitaxial lattice mismatched heterointerfaces between layered semiconductors and themselves and II-VI semiconductors (CdS, CdTe), respectively, have been prepared and their band lineup determined by photoemission. Different physical mechanisms, which govern the heterointerface formation, can be discriminated due to the specific properties of the van der Waals (vdW) surface. The interfaces between layered semiconductors mostly follow the electron affinity rule with a small but systematic deviation, which is assigned to the influence of interfacial quantum dipoles. However, the band lineup to the II-VI semiconductors shows a large interface dipole, which is related to a structural dipole from the polar, Cd terminated, face of the (111)- in case of Zinkblende CdTe- and the (0001)- in case of Wurtzite CdS- oriented overlayer film.

ZnSe/GaAs heterojunctions were investigated by contactless electroreflectance and photoreflectance techniques. Negative surface charge densities on the order of 1012 cm-2 were observed for films grown on n-type GaAs indicating a large contribution to the conduction band barrier between the materials due to band bending. The conduction band offset was also measured using a new photoreflectance technique involving a tunable pump laser.

Contactless electroreflectance measurements at 300 K were performed on two InxGal-xAs/InP ]x = 0.53 (lattice-matched) and 0.75] samples containing three quantum wells (QWs) grown by gas-source molecular beam epitaxy. The spectra consisted of two excitonic transitions (le-l hh and le-l lh), corresponding to the fundamental conduction to heavy (h)- and light(l)- hole transitions, respectively, in the QW portion and a complicated Franz-Keldysh oscillation (FKO) pattern originating in the InP regions. Comparison between the experimental energies of le-l hh/le-llh and a theoretical envelope function calculation (including the effect of strain) made it possible to evaluate the conduction band offset parameters Qc =0.34+0.03 and 0.57+0.03 for x = 0.53 and 0.75, respectively. The InP related FKO beat patterns were analyzed by a Fourier transform method. It was found that the FKO spectra were due to the simultaneous contribution of at least three different fields (106 kV/cm, 36 kV/cm, and 23 kV/cm), which originate in the various interfaces, i.e., substrate/buffer, cap layer/surface, and buffer/QW structure. Identification of the different fields has been accomplished by comparison of the Fourier-transformed spectra before and after sulfur passivation of the structure surface.

We report on the optical investigations of InAs growth on GaAs. In-situ STM/AFM studies show the presence of features 2-4 ML high, which we call quasi-3D (Q3D) clusters, well in advance of 3D island formation. Though the photoluminescence (PL) emission from these Q3D clusters is in the same wavelength regime as that from well developed 3D islands, they show characteristic differences in the PL excitation spectra and temperature dependence of PL, distinguishing them clearly from the 3D islands. Finally, we discuss the lasing observed from lasers containing single and five sets of InAs layers grown with conditions in which the in-situ STM/AFM studies show only 3D islands.

Non-destructive silicon epitaxial film thickness measurements have been performed using spectroscopic ellipsometry (SE) in the visible to near infrared range. The epitaxial films were grown by CVD at 700 – 900°C. It is shown that SE can simultaneously determine the epitaxial film thickness, the native oxide thickness, and the substrate dopant concentration. The epitaxial film thicknesses measured by SE are in excellent agreement with results of secondary ion mass spectrometry (SIMS). The dopant concentrations measured by SE also agree well with SIMS results for n-type substrates, but are consistently higher than SIMS values for p-type substrates. This study shows that spectroscopic ellipsometry could be used in semiconductor manufacturing environments as a viable non-destructive technique for sub-0.5 μm silicon epitaxial film thickness measurement.