Timothy J. Anderson

A binary database for III–V compound semiconductor systems

Abstract A thermodynamic database for binary III-V semiconductor systems has been compiled. It is based upon individual assessments which have been or will be published separately, but each assessment is based on the SGTE recommendation for the pure elements and uses the same solution model expression. The 15 possible binary systems between the group III elements Al, Ga and In on one hand, and the group V elements As, Sb and P are included.

Device modeling and simulation of the performance of Cu(In1−x,Gax)Se2 solar cells

Device modeling and simulation studies of a Cu(In1� x,Gax)Se2 (CIGS) thin film solar cell have been carried out. A variety of graded band-gap structures, including space charge region (SCR) grading, back surface region grading, and double grading of the CIGS absorber layer, are examined. The device physics and performance parameters for different band-gap profiles were analyzed. Based on the simulation results, an optimal graded band-gap structure for the CIGS solar cell is proposed. The performance of the optimally graded band-gap cell is superior to that of the uniform bandgap cell. The SCR grading of the CIGS absorber layer improves the open-circuit voltage (Voc) without significantly sacrificing the short-circuit current density (Jsc) compared to the uniform band-gap CIGS. The back surface grading enhances both Voc and Jsc. An optimal graded band-gap profile, such as a double grading consisting of the SCR grading and back surface grading, improves significantly the efficiency up to 19.83% AM1.5G compared to the uniform bandgap profile with 15.42% efficiency. A comparison of the simulation results with published data for the CIGS cells shows an excellent agreement of photo-current density–voltage and quantum efficiency characteristics. � 2003 Elsevier Ltd. All rights reserved.

Ir/TaN as a bilayer diffusion barrier for advanced Cu interconnects

The properties of an Ir (5nm)∕TaN (5nm) stacked layer as a copper diffusion barrier on Si have been investigated. Ir∕TaN bilayer barriers were prepared at room temperature by magnetron sputtering followed by in situ Cu deposition for diffusion tests. Thermal annealing of the barrier stacks was carried out in vacuum at high temperatures for 1h. X-ray diffraction patterns, cross sectional transmission electron microscopy images, and energy-dispersive spectrometer line scans on the samples annealed at 600°C revealed no Cu diffusion through the barrier. The results indicate that the Ir∕TaN bilayer is an effective diffusion barrier for copper metallization.

Pt-coated InN nanorods for selective detection of hydrogen at room temperature

Single crystal InN nanorods were successfully grown on c‐Al2O3 by hydride-metalorganic vapor phase epitaxy. The measured resistance of bare InN nanorods does not change upon exposure to hydrogen ambient. The addition of sputter-deposited clusters of Pt onto the surface of the InN nanorods, however, produced a significant change in the measured room temperature resistance. The measured resistance changed systematically by 0.5%–12% as the ambient hydrogen concentration in N2 was varied between 10 and 250 ppm after 15 min exposure time. Importantly, a relatively low power consumption of ∼0.3mW was measured under these conditions. There was no response at room temperature to O2, N2O, or NH3 exposures.

The measurement of deep level states caused by misfit dislocations in InGaAs/GaAs grown on patterned GaAs substrates

Rectangular Schottky diodes were fabricated on In0.06Ga0.94As grown by organometallic vapor phase epitaxy on GaAs substrates patterned with mesas. The density of α and β misfit dislocations at the strained‐layer interface changed with the size of the rectangular mesas. Since all mesas (four sizes and two orientations) are processed simultaneously, all other defect concentrations are expected to remain constant in each diode. Scanning cathodoluminescence showed that the misfit dislocation density varied linearly with rectangle size. Deep‐level transient spectroscopy showed that an n‐type majority‐carrier trap is present at 0.58 eV below the conduction band with a concentration that increases with increasing α‐type misfit dislocation density. The β misfit dislocation density had no influence the deep level spectra, indicating that this trap is related to the cores of only α‐type misfit dislocations. The capture rate trend corroborates the view that the trap is associated with the dislocation cores and not w...

Epitaxial growth and characterization of CuInSe2 crystallographic polytypes

Migration-enhanced epitaxy (MEE) has been successfully employed to grow epitaxial films of the ternary compound CuInSe2 on (001) GaAs that exhibit distinct coexisting domains of both a nonequilibrium crystallographic structure characterized by CuAu (CA) cation ordering, and the compound’s equilibrium chalcopyrite structure. X-ray diffraction, transmission electron diffraction, and Raman scattering data provide evidence for this structural polytype. Distinctive signatures of the CA polytype are found in the data from each of these methods, and their analyses are consistent with assignment of this crystallographic structure to the P4m2 space group. This structure is found to preferentially segregate into domains that constitute a distinct metastable phase, which may be stabilized by surface kinetic effects favored by the MEE growth process.

MOCVD of tungsten nitride (WNx) thin films from the imido complex Cl4(CH3CN)W(NiPr)

Thin films of tungsten nitride (WNx) were deposited by MOCVD from the single-source precursor Cl4(CH3CN)W(N i Pr). Films were analyzed by X-ray diffraction (XRD), Auger electron spectroscopy (AES) and cross-section scanning electron microscopy (X-SEM), while the film resistivity was determined by four-point probe. Film growth rates ranged from 10 to 27 ( A/min within a temperature range of 450–7001C. The apparent activation energy for film growth in the kinetically controlled regime was 0.84 eV. Films grown at temperatures below 5001C were amorphous, with minimum film resistivity and sheet resistance of 750mO cm and 47O/&, respectively, occurring for deposition at 4501C. r 2002 Elsevier Science B.V. All rights reserved.

Robust detection of hydrogen using differential AlGaN∕GaN high electron mobility transistor sensing diodes

The use of AlGaN∕GaN high electron mobility transistor (HEMT) differential sensing diodes is shown to provide robust detection of 1% H2 in air at 25°C. The active device in the differential pair is coated with 10nm of Pt to enhance catalytic dissociation of molecular hydrogen, while the reference diode is coated with Ti∕Au. The active diode in the pair shows an increase in forward current of several milliamperes at a bias voltage of 2.5V when exposed to 1% H2 in air. The HEMT diodes show a response approximately twice that of GaN Schottky diodes, due to the presence of piezoelectric and spontaneous polarization in the heterostructure. The use of the differential pair removes false alarms due to ambient temperature variations.

Properties of W-Ge-N as a diffusion barrier material for Cu

The properties of W–Ge–N thin films are reported, focusing on issues relevant to their use as diffusion barriers for Cu metallization on silicon. The amorphous W–Ge–N thin films were deposited on thermally grown SiO 2 / Si using reactive sputter deposition. This was followed by in situ deposition of Cu films. Annealing studies for W–Ge–N were then carried out in a vacuum to investigate Cu diffusion and barrier film crystallization. X-ray diffraction was used to assess the crystallinity of the films upon annealing. The results show that W–Ge–N has a recrystallization temperature that is higher that that for WNx. Auger electron spectroscopy was used to measure the depth profile of Cu diffusion through the barrier layer. Little or no Cu diffusion was detected for a relatively high annealing temperature. The W–Ge–N films were conductive, although the resistivity is somewhat higher than that for WNx. The results suggest that W–Ge–N may be an attractive diffusion barrier material for Si or SiGe devices.

Band-edge electroluminescence from N+-implanted bulk ZnO

N+ ion implantation at moderate doses (1013–1014cm−2) into nominally undoped (n∼1017cm−3) bulk single-crystal ZnO substrates followed by annealing in the range 600–950°C was used to fabricate diodes that show visible luminescence at 300K and band-edge electroluminescence at 120K (∼390nm) under forward bias conditions. The current-voltage behavior of the diodes are characteristic of metal-insulator-semiconductor devices and suggest the implantation creates a more resistive region in the n‐ZnO in which holes are created by impact ionization during biasing, similar to the case of electroluminescence in ZnO varistors. The series resistance is only 25Ω due to the use of the conducting ZnO substrate.