We are examining dry processes for wafer cleaning and producing patterned thin films of metal oxides. This research focuses on determining the kinetics and mechanism of the reaction between ß-diketones and selected metal oxides. Preliminary experiments indicated that CuO, MgO, PbO and ZnO all react readily with 1,1,1,5,5,5-hexafluoroacetylacetone (hfacH). Thin films of CuO and MgO were fabricated via pulsed laser deposition, characterized by various analytical techniques such as Rutherford Backscattering Spectrometry and Scanning Electron Microscopy, etched using hfacH, and then further characterized. Etching rates for CuO and MgO were measured in order to develop a mechanistic understanding of the reaction.

A study of the effect of dopant incorporation on the growth of InGaP by low pressure metalorganic chemical vapor deposition has been performed, in which diethylzinc (DEZn) and H2Se are used as p and n-type doping sources, respectively. The enhancement of interdiffusion, i.e., the disordering of a InGaP layer has been observed due to the introduction of Zn into the growth layer, as indicated by the decrease of intensity of the extra spots on TEM diffraction results. In addition, streaky and wavy diffraction pattern for Se-doped layer reveals the formation of anti-phase domains on a growth layer. According to PL measurement, the emission energy of the grown layer is a function of doping concentration, for which the energy shift as high as 141 meV has been obtained at heavily zinc doping concentration. Therefore, by varying the doping concentration, energy shift can be controlled, providing a potential for its application in optical devices.

A GaAs/Ga1−xA1xAs-superlattice was investigated using quasi-cw PL measurements at T=2 K. The relevant sample parameters were determined by X-ray diffraction: barrier thickness - 5 nm, qw-thickness - 5 nm, x = 0.41. A series of PL-spectra at medium, but constant excitation intensity for different excitation energy (from 1.64 eV to 2.1 eV) was measured. From the high-energy slope of the PL-spectra the electron-temperature Te was determined. A clearly structured dependence of Te on hvexc (excitation energy) was found. We assumed the pronounced structures of the Te - hvexc - hvexc - “spectrum” to be the onset-energies of new, for lower excitation energies not possible relaxation processes. Calculating the excess energy for each kind of carriers (heavy and light holes and electrons) separately, we found δEv=( 0.18 ± 0.05) ∆Eg for the investigated sample. Using this new experimental method one also is able to obtain the energies of higher electronic states (for example Γ → L -transitions) of GaAs/(Ga,Al)Assuperlattices.

In this paper, we present results of our investigations on some aspects of the DX centers. It is shown from the low temperature Hall mobility measurements that the charge state of the DX center is neutral supporting the positive U model for the DX center. Hall and DLTS measurements on Al-rich Al0.8Ga0.2As:Te sample show a reversal in the ordering of the energies of the hydrogenic and deep states of the Te donor, with the DX state lying higher than the X valley related effective mass state. Thermal emission properties of the pressure induced DX states of Ge and Se donors in neutron transmutation doped (NTD) GaAs are discussed.

The ability to produce semiconductor structures with arbitrary vertical composition profiles offers the device physicist new freedom in device structure design. We report on the incorporation of the in-situ sensor technique of desorption mass spectrometry (DMS) in a realtime feedback loop for the continuous control of desorption rates. Assuming previous knowledge of relevant incident fluxes, this technique provides for continuous determination of the composition of the outermost layer of the growing crystal. Using AlGaAs growth as an example, the Ga desorption rate Fd(Ga) is monitored continuously during growth, providing an accurate measure of Al-fraction in the topmost layer of the growing film. By comparing the measured and desired Fd(Ga), an error signal is generated and minimized by varying an appropriate growth parameter. Structures which are vertically graded in composition are produced by programming a varying Fd(Ga) versus time profile. Both substrate temperature Ts and incident arsenic flux Fi(As2) affect Fd(Ga) in a controllable way. Thus, two distinct control loops are constructed based on variable Ts and Fi(As2), respectively. As demonstration vehicles, graded AlGaAs structures with linear, parabolic, sawtooth, and sinusoidal compositional profiles have been produced and characterized. Additionally, we discuss some of the limitations of this technique and its applicability to other materials.

The analysis of SI-GaAs passivated with different plasma treatments by isothermal PITS measurements shows the ability of this technique for the characterization of the electrical effects of the surface treatments. PITS spectra show, in addition to a midgap level assigned to EL2, a non exponential peak which strongly depends on the passivation process. This is related to the generation of defects during the surface processing, likely through the presence of interaction processes involving mid-gap related levels. The comparison between the spectra with different passivation conditions suggests the presence of ionized species in the plasma treatment and the fast growth rate of the passivation layer to determine a higher generation of these process related defects.

It was observed that carrier concentration depth profiles under 200μm-diameter gold Schottky electrodes of deeply Si-implanted electrically active layers on undoped semi-insulating GaAs wafers depend on melt composition of liquid-glass encapsulation Czochralski technique (LEC) growth, Fourier-transformed infrared (FT-IR) measurement carbon content of LEC growth, and consecutive cooling thermal cycle of LEC growth. In the range of this experiment, for head position of boules and 2.5 × 10exp.12/cm2 Si dosage, peak carrier concentrations of As-rich melt LEC growth (initial: [As]/([As]+[Ga])≃0.526) were comparable to or slightly higher than those of near-stoichiometric melt LEC growth. For tail position and 3 × 10exp.12/cm2 Si dosage, a peak carrier concentration of a father As-rich melt LEC-growth was clearly higher than that of Ga-rich melt LEC-growth. LEC-grown melt composition effect depended on consecutive cooling thermal cycle. For peak carrier concentration dispersion of head position, there was anticorrelation between carbon content of FT-IR measurement and peak carrier concentration dispersion.

In this paper we have studied the Einstein relation for the diffusivity-mobility ratio in III-V superlattices with graded structures under magnetic quantization by formulating a new dispersion law. It is found, taking InAs/GaSb an example that the diffusivity mobility ratio increases in an oscillatory way with increasing carrier degeneracy as a consequence4SdH effect. The Einstein relation in IIIV superlattice is greater than that of the same for the constituent materials. Besides the theoretical results are in agreement with the suggested experimental method of determining the same ratio in degenerate materials having arbitrary dispersion laws.

A selective growth of GaAs micro crystals was demonstrated on a Se-terminated GaAIAs surface by sequential supplies of Ga and As molecules for the quantum well box structure. After the growth, the surface consisted GaAs micro crystals with (111) facets and some Se clusters. The cross sectional investigations by the high resolution electron microscope revealed an epitaxial growth of GaAs micro crystals on the surface and a mixture of Ga2Se3 and A12Se3 layer formation at the interface of GaAs/Se-terminated GaAIAs. The selenidation process seems to be a reaction limited one. The Se cluster segregation could be avoided by selenidation in As molecule atmosphere.

Shutter closure during MBE deposition causes source overheating and results in flux transients. These transients are particularly detrimental to the thickness and compositional accuracy of thin quantum well layers. In this paper, we document the effects of flux transients on growth of multiple quantum well (MQW) and resonant tunneling diode (RTD) structures, and demonstrate rudimentary transient correction by employing real-time flux detection.

Reflection mass spectrometry (REMS) provides a convenient in situ method for MBE flux monitoring. The Group III partial pressures can be detected in the presence of Group V overpressure, and REMS is compatible with wafer rotation. We used REMS to characterize In, Al and Ga flux transients as a function of shutter closed time, cell flux and substrate temperature. Overshoot magnitudes up to 30% were observed. We verified the correspondence of REMS signal transients and effusion cell flux transients using GaAs/AlGaAs and InGaAs/lnAlAs MQW and test structures. We also successfully demonstrated flux transient correction by cell temperature ramping during MQW and RTD growth.

Not all threshold voltage (Vth) scattering of Si-implanted metal-semiconductor field- effect- transistors (MESFETs) on low dislocation density and semi-insulating (S.I.) liquid- glass encapsulation Czochralski (LEC) GaAs crystals grown at relatively high pull-speed were small. By comparison with the Lang x-ray topographs of the wafers, it was found that x-ray topograph contrast variations reflected on the films did not correspond with Vth variations of the wafers at all. Especially, in low dislocation density regions, which are in white regions on the films of the x-ray topographs, very large Vth turbulences were observed. We believe that dislocation-less in LEC GaAs crystals causes large Vth turbulences of Si-implanted MESFETs and that frozen cell-lattice-structure large turbulences by pinning centers associated with vacancies like glass cause large Vth turbulences.

Thin film of GaAs/AlGaAs multiple quantum well (MQW) structure have been bonded to the lithium tantalate (LiTaO3) or calcium carbonate (CaCO3) substrates cut such that one of the linear thermal expansion coefficients almost matches that of the MQW while its orthogonal counterpart does not. By choosing the proper bonding and operating temperatures, in-plane anisotropic strain up to 0.3% has been achieved. The transmission spectrum shows an anisotropy in excitonic absorption which results in a polarization rotation of a light beam at normal incidence to the structure. The theoretical calculation is in agreement with the experimental results. Using the polarization rotation, we have demonstrated a novel MQW light modulator with an exceedingly high contrast ratio of 330:1.

The feasibility of using isothermal RTA in annealing ion implanted layers for forming junctions has been investigated for the past 10 years. While many of the scientific details surrounding defect formation, transient diffusion and dopant activation remain to be clarified, RTA intrinsically is a viable annealing process which is essential for fabricating advanced silicon devices.

Strained-layer semiconductors have revolutionized modern heterostructure devices by exploiting the modification of semiconductor band structure associated with the coherent strain of lattice-mismatched heteroepitaxy. The modified band structure improves transport of holes in heterostructures and enhances the operation of semiconductor lasers. Strainedlayer epitaxy also can create materials whose band gaps match wavelengths (e. g. 1.06 μm and 1.32 μm) not attainable in ternary epitaxial systems lattice matched to binary substrates. Other benefits arise from metallurgical effects of modulated strain fields on dislocations.

Lattice mismatched epitaxial layers that exceed the limits of equilibrium thermodynamics will degrade under sufficient thermal processing by converting the as-grown coherent epitaxy into a network of strain-relieving dislocations. After presenting the effects of strain on band structure, we describe the stability criterion for rapid-thermal processing of strained-layer structures and the effects of exceeding the thermodynamic limits. Finally, device results are reviewed for structures that benefit from high temperature processing of strained-layer superlattices.

SiO2 thin films were deposited by remote PECVD on Si surfaces exposed to species generated in O2/N2 and O2/NH3 plasmas. The surface chemistry was studied by Auger Electron Spectroscopy, AES, and the electrical properties of the SiO2/Si interface by high frequency and quasi-static Capacitance-Voltage, C-V, measurements. The AES results showed that Ccontamination was removed by exposure to both plasma-excited gas mixtures, but that N-atoms were incorporated into the SiO2 film, and Si-N bonds were formed at the SiO2/Si interface. C-V measurements indicated that the Si-N bonding structure, rather than the N-atom concentration, is critical in determining the interface electrical properties. The effects of Rapid Thermal Annealing, RTA, on the electrical properties of these SiO2/Si interfaces were also studied.

Rapid thermal annealing (RTA) has been employed for the electrical activation of shallow n-channel layer by Si+ implantation in the fabrication of GaAs MESFET. To prevent considerable outdiffusion of gallium and arsenic from GaAs substrate during annealing, encapsulating layers such as SiNx and SiNx/SiO2 are deposited. The SiNx/SiO2 double dielectric encapsulant is shown to be more effective to improve the electrical activation. Depending on RTA temperature between 900 and 950°C, the maximum activation efficiency exhibits 77% at the implanted energy of 70 keV and the dose of 5×1012 cm−2. SIMS analyses show the reduction of the hydrogen contained in the silicon nitride and no outdiffusion of Ga and As during RTA. It also shows the sharp Si-profile after RTA at 950°C, 30 sec. The MESFET fabricated using activaton with RTA provides better transconductance than that with furnace-annealed activation.

A combination of i) low-temperature, 300-400°C, plasma-assisted oxidation to form the SiO2/Si interfaces, and ii) 800°C rapid thermal chemical vapor deposition, RTCVD, to deposit SiO2 thin films have been used to fabricate gate-oxide heterostructures. This sequence separates SiO2/Si interface formation by the oxidation process from the deposition of the bulk oxide layer by RTCVD. These two processes were performed in situ and sequentially in a single-chamber, ultraclean quartz reactor system. We have studied the chemistry of the interface formation process by Auger electron spectroscopy, AES, and the electrical properties of MOS devices with Al electrodes by C-V techniques.

Process modules for MOS gate fabrication were developed which can be completed subsequently in one RTP reactor: atmospheric process sequences for gate oxides and oxynitrides as well as low pressure chemical vapor deposition of polysilicon (RTCVD). Prior to the Rapid Thermal Oxidation (RTO), the wafers were treated with a Rapid Thermal Cleaning process (RTC) in H2/Ar ambient. After the desoxidation step the RTO was done in O2/H2/Ar followed by an anneal (RTA) for the gate oxide or a nitridation in NH3 (RTN) and reoxidation for the oxynitrides, respectively. The polysilicon gate electrode was fabricated either by RTCVD in situ or in a conventional furnace reactor. The two-step RTCVD process resulted in a very good thickness uniformity for the polysilicon layers of 3% (3mm from the edge). The influence of the process variations on breakdown field, fixed oxide charge, interface state density, flatband voltage, and threshold voltage of the different types of gate dielectrics was investigated. The charges and voltages were determined by LF-HF CV measurements. In order to characterize the radiation tolerance of electronic devices, radiation induced flatband and threshold voltage shifts as well as the build up of interface charges were determined. The irradiation was performed at a Co - 60 gamma source. Breakdown fields in the range of 19 MV/cm, interface state densities of less than 109 eV−1cm−2, and radiation induced threshold voltage shifts below 0.1 V after 1.5 Mrad(Si) were obtained.

High quality InP and In0.53Ga0.67As undoped and Zn-doped layers were grown by means of rapid thermal low pressure metalorganic chemical vapor deposition (RTLPMOCVD) technique, using tertiarybutylphosphine (TBP) and tertiarybutylarsine (TBA), as the phosphorus and arsenic sources. The InP films were grown at a P:In ratios of about 75 and the InGaAs films were grown at a As:In ration of about 2, low temperatures at the range of 450-550°C, pressures it the range of 1-4 tons, and growth rates of 2-3 nm/sec. All the film growth conditions were optimized to yield defect-free layers with featureless morphology, which reflected at a minimum backscattering yield (Xmin) as low as 3.1% for the InP and 3.6% for the InGaAs. These films presented a good electrical properties, as well, with hole mobility of 4200 cm2/Vs for the undoped-InP layers and 75 cm2/Vs for the undoped-InGaAs layers.

The HBTs used in this study were grown by OMVPE. The base was carbon doped to 3×1019 cm−3 and the base thickness was 500Å. Several 3μ ×10μ HBTs were biased at Ic =2,4 and 10mA (VCE=2V) and maintained at TA=125°C. Based on 1000 hours of operation at 125°C, Ic =2mA is safe, Ic =4mA is marginal and Ic =10mA is fatal.