H.M. Dauplaise

Indium phosphide passivation using thin layers of cadmium sulfide

The electrical properties of the silicon dioxide/n‐type (100) InP interface were significantly improved by thin interlayers of chemical bath deposited CdS. The CdS layer and CdS/InP interface were investigated with x‐ray photoelectron spectroscopy (XPS) and photoluminescence (PL). XPS data showed reduction of native oxides and the prevention of subsequent substrate oxide growth following CdS layer deposition. PL spectra, measured between 1.0 and 1.3 μm, indicate a reduction in phosphorus vacancies. Metal–insulator–semiconductor (MIS) capacitors fabricated with CdS‐treated InP substrates displayed interface‐state densities below 1×1011 eV−1 cm−2 when determined from the difference between the high‐ and low‐frequency capacitance data.

Analysis of thin CdS layers on InP for improved metal–insulator–semiconductor devices

Cadmium sulfide (CdS) layers were deposited from an aqueous solution of thiourea, cadmium sulfate, and ammonia on (100) n‐InP at 60–95 °C. X‐ray photoelectron spectroscopy showed that the deposition process effectively removes native oxides on InP and forms a protective layer for subsequent dielectric deposition. Surface analysis also showed that the InP surface is not P deficient following oxide deposition on CdS‐treated InP. Capacitance–voltage and conductance–voltage measurements of metal–insulator–semiconductor (MIS) capacitors were used to compare samples with and without CdS films between InP and a deposited insulator. Capacitance–voltage response of CdS‐treated MIS structures showed well‐defined regions of accumulation, depletion, and inversion. The interface‐state density at midgap was reduced from 5×1011 to 6×1010 eV−1 cm−2 with CdS treatment. Depletion‐mode MIS field‐effect transistors made using this new passivation technique exhibited superior device performance to that of untreated samples.

Optimization of Chemical Bath‐Deposited Cadmium Sulfide on InP Using a Novel Sulfur Pretreatment

A thiourea/ammonia pretreatment followed by chemical bath deposition of cadmium sulfide was used to passivate the surface of indium phosphide (100). The pretreatment was shown by X‐ray photoelectron spectroscopy to effectively remove native oxides from the InP surface and form an indium sulfide layer. The subsequent chemical bath deposition of CdS on a sulfur‐passivated surface forms a stable layer that protects the substrate from oxidation during chemical vapor deposition of . The passivation process was optimized for electrical response by varying the reactant concentrations of the chemical bath. Reflection high‐energy electron‐diffraction (RHEED) analysis showed that the pretreatment results in a (1 × 1) surface, which reconstructs to (2 × 1) after heating in vacuo to 200°C. RHEED and atomic force microscopy showed an increase in CdS surface roughness with increasing thickness corresponding to the formation of oriented surface asperities. CdS‐passivated metal‐insulator‐semiconductor diodes exhibited a density of interface states of when calculated by the high‐low method, more than one order of magnitude lower than the of untreated metal‐insulator‐semiconductor samples. A CdS layer thickness of ~ 10 A was determined to yield optimal capacitance‐voltage response for all CdS deposition conditions investigated.

Cadmium sulfide surface stabilization for InP-based optoelectronic devices

Thin layers of chemical bath deposited cadmium sulfide were used to improve the surface and interface properties of InP and its latticed-matched III-V compounds. X-ray photoelectron spectroscopy indicates chemical reduction of surface oxides and the prevention of subsequent group III or V oxide formation. Photoluminescence spectra, measured between 1.0 and 1.3 μm, indicate a dramatic reduction in phosphorus vacancies following CdS treatment. Metalinsulator-semiconductor capacitors fabricated onn-type InP substrates with CdS interlayers display near-ideal quasi-static response and interface-state densities in the low 1011/eVcm2 range. Thin CdS layers were used to passivate the surface of InAlAs/InGaAs high electron mobility transistors (HEMTs) and metal-semiconductor-metal (MSM)photodetectors.AfterCdS treatment, Schottky diode barrier heights of 0.6 eV were regularly obtained. For HEMTs, drain-togate current ratios of 8 × 104 were observed after CdS treatment. For a new backside illuminated MSM design, the dark current of CdS-treated samples was reduced three orders of magnitude to below 1 nA.

Optoelectronic properties of transition metal and rare earth doped epitaxial layers on InP for magneto-optics

Rare earth-and transition metal-doped thin films of InP, In0.53Ga0.47As, and In0.71Ga0.29As0.58P0.42 were grown by liquid phase epitaxy and evaluated for use in integrated electro-optical and magneto-optical applications, such as waveguides and Faraday rotators. The films were lattice matched to (100) InP substrates, and the transition metal (Mn) and rare earth (Gd, Eu, and Er) doping concentra-tions were between 2.6 × 1018 and 1.5 × 1020 cm-3. The chemical profiles were generally found to be homogeneous by SIMS, although in more highly doped films the rare earths were observed to segregate toward the interfaces. The undoped films were n-type, and the net carrier concentrations in the rare earth-doped (Gd, Eu, Er) films were decreased by an order of magnitude. The Mn-doped films were p-type. Optically, the rare earth dopants were observed to raise the refractive index of the layers at 632.8 nm, and subsequent waveguiding in doped InP layers was observed at 1.3 μm. Although the Faraday rotations of our materials were much less than that of well known oxides, such as yttrium iron garnet, they were sufficient for device applications, and our materials can be much more easily integrated with InP OEIC devices. For example, a 1 cm waveguide would provide the large rotation (45°) required in isolator applica-tions.

Structural and Electrical Properties of Low‐Temperature, Low‐Pressure SiO2 on Si

The physical and electrical properties of SiO 2 deposited on Si at low pressure -2-10 Torr) and low temperature (100-300°C) are reported. Fourier transform infrared spectroscopy (FTIR) is used to examine the chemical nature of the deposited oxide as a function of deposition and anneal temperature. Films deposited at T<200°C reveal partially oxidized silicon along with water and silanol groups. As the deposition temperature is raised to 300°C, the FTIR spectra resemble that of thermal oxide. Annealing of films deposited at lower temperatures significantly improves the films, also causing the FTIR peaks to resemble those of thermal oxide. Capacitance-voltage measurements are used to extract fixed-charge and interface-state densities. Fixed-charge densities below 1×10 11 cm −2 and interface-state densities 5×10 10 cm −2 eV −1 are obtained after rapid thermal annealing of SiO 2 on SI

Thermal Desorption Spectroscopy of Sputtered MoSx Films

Thermal desorption spectroscopy (TDS) is introduced as a diagnostic tool for determining the thermal stability of solid lubricant films. In particular, TDS revealed the temperatures at which various decomposition processes occurred as sputtered films were heated in vacuum. The primary film decomposition products detected were SO2 beginning at about 425K, and S2 beginning at about 1150K. A close relationship between water desorption beginning about 400K and SO2 desorption exists in the temperature range 400K-800K. Besides chemical decomposition products, a significant amount of argon trapped in the film during the sputtering process is released at various temperatures. TDS results for sputtered films were compared with results for burnished films and with thermo-gravimetric (TGA) analysis, water adsorption, and other relevant studies of molybdenum disulfide found in the literature. TDS also showed that N+ ion-beam modification of sputtered films resulted in a decrease in desorption of SO2. Along with TDS, ...

Inverted, substrate-removed MSM and Schottky diode optical detectors

The InGaAs metal-semiconductor-metal (MSM) photodetector is a high-performance component for lightwave communication systems. Low capacitance, dictated by finger spacing, and high carrier drift velocity result in GHz operating bandwidths. Efficient optical absorption to 1.7 /spl mu/m results in high responsivity at the wavelengths preferred for optical fiber communications, 1.3 and 1.5 /spl mu/m. Simple processing steps make the MSM practical for monolithic integration with low-noise, high electron mobility transistor (HEMT) receiver amplifiers and other opto-electronic circuit applications.

ELECTRICAL CHARACTERIZATION OF CDS PASSIVATION ON INP

InP surface passivation has been realized by a convenient chemical bath deposition (CBD) of a thin CdS layer. For comparison, samples without any treatments and/or with only a thin SiO2 layer were also prepared. Also studied was the effect of a thin layer of SiO2 deposited immediately after the CdS deposition. Schottky contacts were made on the CdS-passivated InP by electron-beam deposition of Ti/Au. Electrical characterization was conducted by current-voltage (I-V) and current-voltage-temperature (I-V-T) measurements. It was found that the electrical performance of the Schottky contacts of the CdS-passivated InP samples was improved significantly. The thickness (deposition time) of the CdS strongly affects the device electrical performance. The additional SiO2-on-CdS layer plays a key role in the process of InP surface passivation. Post-treatment in the CdS deposition process also strongly affects the surface morphology and electrical properties. Surface morphology studied by atomic force microscopy (AFM) indicates that the surface roughness increased after CdS deposition, though the degree of roughness is reverse proportional to the CdS process time. X-ray photoelectron spectroscopy (XPS) shows that the CdS layer protects the InP substrate during the oxide deposition.

Cadmium sulfide surface stabilization and Schottky barrier enhancement for InP based optoelectronic devices

We have investigated the use of CdS interlayers grown by chemical bath deposition (CBD). We have deposited CdS on a wide variety of III-V semiconductors. We found that native oxides were reduced by the CdS treatment. CdS-treated and untreated HEMTs and metal-semiconductor-metal photodetectors (MSMs) were compared. Thin 50 /spl Aring/ layers were effective in reducing gate and surface leakage. The thin CdS layers reduced the gate leakage of InA1As/InGaAs HEMTs and the dark current of InA1As/InGaAs optical detectors. X-ray photoelectron spectroscopy indicates a reduction of surface oxides and the prevention of subsequent group III or V oxide formation. Backside processing of InGaAs/lnA1As MSMs allows complete coverage of the mesas. The CBD process for depositing CdS is inherently adaptable to a wide range of optoelectronic device processes.