We present a detailed and comprenhensive theoretical investigation of the sulphur-passivated (001) surface of InP. First, the ground-state structure is determined using density-functional methods, including full relaxation of the surface. The lowest-energy structure at 0 K is a striking (2 × 2) reconstruction with the S atoms displaced from the bridge sites to form short and long dimers, belonging to two distinct sublayers. This surface structure is used to calculate the backscattering Raman spectrum; the two peaks arising from surface-layer vibrations predicted by our calculations are observed. Next, our first-principles calculations are extended to the study of a number of other stable states of the surface that can arise upon annealing. For this purpose, we construct and relax several higher-energy states of the surface, and calculate the corresponding core-level photoemission spectra. A remarkable sequence of structures is found to unfold from the fully S-covered ground state as they become energetically accessible. The surface S atoms exchange with bulk P atoms, forming new (and strong) S-P bonds while dissociating pre-existing S–S dimers. The predicted core-level spectra are found to be entirely consistent with the experimental measurements; our calculations indicate that the annealed (at about 700 K) surface is a (2 × 2) structure containing two S and two P atoms per unit cell. Finally, we have used the predicted stable surface structures to calculate the photoemission and inverse photoemission spectra. They are found to agree well with experiment if the surface is assumed to consist of a mixture of the above ground-state and annealed structures.

An ammonia-based, in situ passivation of GaAs surfaces conducted within a metalorganic vapor phase epitaxy reactor is present. The shift of the GaAs surface Fermi level, and hence the surface charge density, resulting from this in situ passivation, has been studied using photoreflectance (PR) spectroscopy. Samples consisting of an undoped GaAs layer on highly doped n-GaAs (UN+) and p-GaAs (UP+) structures allow for the exact determination of the surface Fermi level position using PR These structures were grown by MOVPE and in situ thermal nitridation was performed after growth within the MOVPE system without exposure to the air. After nitridation, the surface Fermi level can be shifted by ∼ 0.23 eV towards the conduction band edge for UN+ structures and by ∼ 0.11 eV towards the valence band edge for UP+ structures from the normally mid-gap ‘pinned’ positions.

We have studied the single-crystal Gd2 O3 films grown epitaxially on GaAs(100) substrate with single-crystal x-ray diffraction. The sesquioxide Gd2 O3 forms two hexagonal phases, one monoclinic and one cubic phase in bulk form. In our studies of different thickness films, we have found that the Gd2 O3 grows only in the cubic phase with a unique epitaxial orientation. The two-fold (110) planes of the Gd2 O3 are oriented parallel to the four-fold GaAs(100) surface, while alligning its [001] and [110] axes with the [011] and [011] axes of GaAs within the plane, respectively. The film chooses only one of the two such possible orientations, which can be explained by the local bonding configuration at the interface. We find evidence for an elastic strain in the films less than 50 A thick.

The structure of monolayer-passivated single crystal semiconductor surfaces has been studied using synchrotron radiation X-ray absorption fine structure spectroscopy (XAFS). The near edge and extended fine structure signals, supported in some cases by first-principles calculations, have been used to investigate Ge(111)-Cl; GaAs(111)-Cl; GaAs(111)A-S, GaAs(111)B-S and GaAs(001)-S. The use of a solid state Ge X-ray fluorescence array detector has led to significant improvements in data quality and thus structural accuracy. The relationship between the derived surface structures and the development of improved passivated surfaces is discussed.

The present status of surface passivation research for III-V compound semiconductors utilizing a novel unique structure including a silicon interface control layer (Si ICL) is presented and discussed. The basic principle of passivation is to insert an ultrathin MBE-grown Si layer between the III-V compound semiconductor and a Si-based thick insulator so as to terminate the surface bonds of the III-V material with Si atoms and then to transfer Si-bonds smoothly to those of the Si based insulator. Based on the calculation of quantized levels in strained Si ICL, the passivation structure was optimized. Such a structure was realized by partial nitridation of Si ICL surface. In-situ surface characterization techniques including newly developed UHV contactless C-V technique, were used for optimization of each passivation step. Surface reconstruction of initial semiconductor surface was found to have a great influence on passivation. In the case of GaAs, the c(4×4) surface is preferable to the (2×4) surface. The novel process has realized the oxide-free surface passivation of InP with a Nssmin value of 2 × 1010 cm−2 eV−1. Furthermore, the novel passivation technique has been successfully applied to the fabrication of MISFETs and IGHEMTs, and the passivation of quantum structures.

Ga2O3(Gd2O3) film was previously discovered to effectively passivate GaAs surface, and the employment of this oxide as gate dielectric has led to the first demonstration of the enhancement-mode GaAs metal oxide semiconductor field effect transistors (MOSFETs) with inversion. In order to gain insight into the passivation mechanism and elucidate the role of Gd2O3, we have carried out a systematic study of the dependence of the structural and dielectric properties of (Ga2O3)1−x(Gd2O3) on the Gd (x) content. Our studies indicate that it is necessary to have the Gd addition exceeding 14% in order to form an electrically insulating dielectric with low interfacial state density. Furthermore, we found that pure Gd2O3 film grows epitaxially on GaAs in the single domain, (110) oriented Mn2O3 structure. This new crystalline dielectric has a dielectric constant ∼10, and shows excellent dielectric properties with low leakage and high breakdown strength even for films as thin as 2.5 nm. We expect that epitaxial growth of the Mn2O3 structure can be extended to other rare earth oxides, and to other semiconductor substrates like Si.

High-density plasma technology is becoming increasingly attractive for the deposition of dielectric films such as silicon nitride and silicon dioxide. In particular, inductively-coupled plasma chemical vapor deposition (ICPCVD) offers a great advantage for low temperature processing over plasma-enhanced chemical vapor deposition (PECVD) for a range of devices including compound semiconductors. In this paper, the development of low temperature (< 200°C) silicon nitride and silicon dioxide films utilizing ICP technology will be discussed. The material properties of these films have been investigated as a function of ICP source power, rf chuck power, chamber pressure, gas chemistry, and temperature. The ICPCVD films will be compared to PECVD films in terms of wet etch rate, stress, and other film characteristics. Two different gas chemistries, SiH4/N2/Ar and SiH4/NH3/He, were explored for the deposition of ICPCVD silicon nitride. The ICPCVD silicon dioxide films were prepared from SiH4/O2/Ar. The wet etch rates of both silicon nitride and silicon dioxide films are significantly lower than films prepared by conventional PECVD. This implies that ICPCVD films prepared at these low temperatures are of higher quality. The advanced ICPCVD technology can also be used for efficient void-free filling of high aspect ratio (3:1) sub-micron trenches.

Selective oxidation of AlAs (or AlGaAs) can be used to form buried, low refractive index apertures within high Q Fabry-Perot microcavities. These apertures provide electrical and optical confinement, and for vertical-cavity surface-emitting lasers (VCSELs) have resulted in ultra-low threshold room temperature lasing with threshold currents under 25 μA. When used with quantum dot light emitters, the oxide-apertured microcavity can also be used to control the spontaneous lifetime. We describe the microcavity fabrication based on high Q Fabry-Perot microcavities and selective oxidation, and design and cavity Q constraints for apertured microcavities for quantum well and quantum dot VCSELs and microcavity LEDs. Threshold current densities of quantum well VCSELs are as low as 98 A/cm2, while ground state lasing is also obtained for quantum dot VCSELs. Our initial experiments on microcavities with very small apertures and quantum dot emitters demonstrate up to a factor of 2.3 increase in the spontaneous emission rate.

Solar cells made from III–V materials have achieved efficiencies greater than 30%. Effectively ideal passivation plays an important role in achieving these high efficiencies. Standard modeling techniques are applied to Ga0.5In0.5P solar cells to show the effects of passivation. Accurate knowledge of the absorption coefficient is essential (see appendix). Although ultralow (<2 cm/s) interface recombination velocities have been reported, in practice, it is difficult to achieve such low recombination velocities in solar cells because the doping levels are high and because of accidental incorporation of impurities and dopant diffusion. Examples are given of how dopant diffusion can both help and hinder interface passivation, and of how incorporation of oxygen or hydrogen can cause problems.

Performance of GaAs-based FETs is strongly affected by the electrical properties of passivated surfaces via the surface charges induced at interface states and at the traps within the passivation films. In order to study these two kinds of sources, a set of new characterization techniques are respectively developed for the GaAs interface system, which is in a largely different situation from that for the SiO2/Si interfaces. Our optical technique based on electroreflectance allows accurate evaluation of interface states and is especially useful for the material systems with strong surface pinning. For the study of trapping centers in CVD dielectrics, use of thermally oxidized Si interfaces is found to be quite convenient. The experimental findings are further discussed in conjunction with FET characteristics and an importance of time-domain control of the surface charges is emphasized in the power FET operation. This concept turns out to be the main motivation of a new MESFET structure with a filed-modulating plate (FPFET) which has achieved a state-of-the-art RF performance based on GaAs.

Mixed types I - type II multiple quantum wells (QW) structures consist of alternating narrow- and wide GaAs wells, separated by AlAs barriers. Transfer of electrons from the narrow- to the wide well results in the formation of a two-dimensional electron gas (2DEG) in the wide wells and a hole gas (2DHG) in the narrow ones. The present study investigated the effect of these gases on the various photoluminescence (PL) bands. The study utilized two modulations techniques: double beam PL and microwave modulated PL (MMPL), offering high-resolution spectroscopy, control of the 2DEG density and effective temperature. The results showed that the formation of a low density 2DEG in the wide wells cause the formation of trions. However, a large density of excess electrons makes mutual collisions with other photo-generated species, causing the dissociation of the trions and excitons. In addition, electrons transfer through the barrier gives rise to barrier-well indirect recombination emission.

The degradation of AlGaAs/GaAs diode laser performance during operation is typically due to catastrophic optical damage of the facets caused when thermal runaway occurs. These heating effects are due to the presence of non-radiative recombination sites at and near the facets. MOCVD GaS is deposited on the facets of 825-nm ridge waveguide AlGaAs/GaAs quantumwell laser diodes as an electronic passivation to reduce the number of surface states available for non-radiative recombination. For passivated devices, a peak pulsed power nearly double that of unpassivated devices was achieved. The passivated devices also exhibit a longer lifetime before degradation. The impact of the passivation process on other optical characteristics of the laser diodes will also be discussed.

We report the energy band offsets at a Ga2O3(Gd2O3)-GaAs interface. The valence-band offset (ΔEv) is ∼ 2.6 eV, measured by soft x-ray photoemission spectroscopy. Analysis of the current-voltage characteristics of a Pt-Ga2O3(Gd2O3)-GaAs MOS (metal-oxide-semiconductor) structure, which are dominated by Fowler-Nordheim tunneling, reveals a conduction-band offset (ΔEC) ∼ 1.4 eV at the Ga2O3(Gd2O3)-GaAs interface and an electron effective mass (m*) ∼ 0.29 me of the Ga2O3(Gd2O3) film.

Silicon nitride (SiNx) films with extremely low interface charge densities have been developed by electron cyclotron resonance-chemical vapor deposition (ECR-CVD) deposition on GaAs substrates. The procedure is a one-step process and does not involve H2 and/or N2 pre-treatment of the sample surface. Characterization by Fourier transform infrared (FTIR) and ellipsometry analysis indicate good properties of the film revealing N-H and Si-N bonds. Results of capacitance-voltage (C–V) measurements show surface charge densities on the order of 5 × 1010 cm−2, which we believe is the lowest surface charge density achieved so far over GaAs.

Oxidation and carbon contamination of n-type GaAs (100) surfaces have been investigated by x-ray photoelectron spectroscopy (XPS), Auger electron spectroscopy (AES) and secondary ion mass spectroscopy (SIMS) for a variety of cleaning and etching pretreatment procedures prior to immersion in either (NH4)2S, Na2S aqueous solutions or S2Cl2 solution in dichloromethane. The study has shown that sulfur passivation removes surface oxide and minimize carbon contamination for surfaces treated in (NH4)2S and S2Cl2 solutions. A significant oxygen and carbon contamination in the anodic passivation of GaAs (100) in (NH4)2Sx aqueous solution have been quantitatively measured. In addition, pretreatment in basic solutions have shown minimal oxygen and carbon level in comparison with the acidic solutions. Surface pretreatment carried out ex-situ has shown a higher risk of surface contamination prior to sulfur passivation.

The presence of DX centers in InxAl1−xAs, primarily in the indirect portion of the InxAl1−xAs bandgap, has been determined using modulation doped InxAl1−xAs/InyGa1−yAs heterostructures by means of persistent photoconductivity (PPC) and galvanomagnetic measurements. From the cooling bias experiment, the PPC, and self consistent Poisson and Schrddinger simulations the ratio of the ionized shallow donors to the DX centers is obtained. Using this ratio in the grand canonical ensemble (GCE) the energy level of DX centers is determined. It is found that the DX energy level merges with the conduction band at x ≅ 0.42 and is resonant with the conduction band in higher indium concentration.

Anodic oxides of SixGe1−x (0 ≤ x ≤ 1 ) alloys have been made by plasma assisted oxidation in a microwave frequency (2.45 GHz) reactor working in the constant current bias mode. Oxide films ∼15 – 40 nm (depending upon the Ge concentration) were obtained in 10 minutes without a temperature rise of the substrate of more than 100 °C. Detailed infrared absorption studies of the oxides enabled the Si-O-Si, Ge-O-Ge and Si-O-Ge vibrational modes to be identified, the strongest being at 1056, 858 and 1000 cm−1 respectively. These modes are associated with the O asymmetric stretch, their values are at lower wavenumbers than in bulk oxides due partly to ultraviolet radiation induced structural modification and partly to thin film optic effects. A statistical model for the different bonds present in SixGe1−xO2, when used to simulate the infrared spectrum does not predict the experimentally observed form, the Ge-O-Ge peak is in general too intense in the experimental spectrum. Auger electron spectroscopy profiling of the SixGe1−x oxides suggests that there is a build-up of Ge close to the surface/oxide interface so that when combined with the infrared data, we conclude that there is a GeO2 rich region at the surface/oxide interface. The oxide is, however, globally stoichiometric. Electrical measurements (C(V) and interface state density) were begun on metal-oxide-semiconductor (MOS) capacitors for Si1−xGex. oxides over the range of concentrations 0 ≤ x ≤ 1. Only Si1−xGex oxides with x≤0.15 appear to yield satisfactory MOS capacitor curves.

There are discussed some fundamental physical aspects of surface manipulation by femtosecond laser pulses. Among touched on problems are formation processes of shock electromagnetic waves and surface ripple structures. Proposed theoretical model of femtosecond laser-pulse interaction with matter is illustrated by results of FDTD modeling of linear and nonlinear light scattering by rough surface. Possibility of surface roughness modification and required for that optimal laser-pulse parameters are discussed on the bases of obtained results.

A method to produce large area indium antimonide thin films through a reaction, Sb2S3 + 2 In → 2 InSb + 3 S↑ is presented. A thin film of Sb2S3 with typically 0.2 μm thickness is produced on glass substrate by chemical bath deposition (CBD) at 10°C using thiosulfatoantimonate(III) complex. Subsequently, a thin film of indium is deposited on the Sb2S3 film by thermal evaporation. Annealing the thin film stack of Sb2S3-In at 300°C in a nitrogen atmosphere produces the InSb thin film. The formation of this film is confirmed by x-ray diffraction studies. We would discuss the optimization of the individual film thickness in the Sb2S3-In stack to produce a thin film of single phase InSb or a heterostructure, Sb2S3-InSb. The electrical and optical properties of the films are presented.

W CVD process was caried out on molecular layer epitaxially-grown GaAs just after in-situ surface treatment under optimized AsH3 pressure followed by ex-situ photolithography process. The precursor for W CVD used is W(CO)6. The W/GaAs interface is analyzed using SIMS and RBS/channeling technique. Interface structure was directly observed by cross sectional HRTEM. Plan view HRTEM observation was also carried out. From these physical analyses, it is shown that the mixed layer at W/GaAs interface is estimated to be about 2–3 ML and that the deposited W layer is epitaxially aligned with underlying GaAs lattice. The contact resistance in W/GaAs is obtained by the transmission line measurements (TLM) of patterned W on heavily doped GaAs grown by (molecular layer epitaxy) MLE. The dependence of the contact resistance on the surface treatment prior to the W CVD is also studied. Barrier height of W/GaAs structure is measured by the temperature dependence of I-V characteristics. Contact resistance of non-alloyed structure achieved are 3 × 10−7 Ωcm2 for n-type GaAs:Te and below 5 ×10−8 Ωcm2 for p-type GaAs:C respectively.