M. S. Carpenter

Bio: M. S. Carpenter is an academic researcher from Purdue University. The author has contributed to research in topics: X-ray photoelectron spectroscopy & Bipolar junction transistor. The author has an hindex of 6, co-authored 6 publications receiving 398 citations.

Effects of Na2S and (NH4)2S edge passivation treatments on the dark current‐voltage characteristics of GaAs pn diodes

Abstract: We have investigated the dark current‐voltage characteristics of GaAs pn homojunctions whose surfaces have been passivated with Na2S and (NH4)2S chemical treatments. Reductions in 2kT perimeter recombination currents by a factor of 3.2 were obtained for the two treatments. A shunt leakage, observed at low forward bias for the Na2S treated devices, is virtually eliminated with the (NH4)2S treatment. It is also shown that even the high quality, large area (0.25 cm2) pn diodes used in this study are dominated by 2kT edge currents before passivation.

Investigations of ammonium sulfide surface treatments on GaAs

Abstract: X‐ray photoelectron spectroscopy (XPS) and reflection high‐energy electron diffraction (RHEED) results are presented for ammonium sulfide treated (100)GaAs surfaces. XPS shows that the sulfur coverage is independent of the ammonium sulfide concentration, although the relative amount of arsenic decreases as the sulfide concentration increases. RHEED patterns show that higher temperatures are required for the surface to restructure following treatment with higher sulfide concentration. In addition to the order of magnitude changes in the diode saturation current densities following ammonium sulfide treatment, we observe that the characteristics of gold and aluminum Schottky barriers on sulfide‐treated GaAs surfaces also vary with the substrate temperature during metal deposition.

X‐ray photoelectron spectroscopy of ammonium sulfide treated GaAs (100) surfaces

Abstract: The effect of an ammonium sulfide treatment on the GaAs (100) surface has been investigated by x‐ray photoelectron spectroscopy. The treatment produces a slight Ga enrichment on the surface and leaves roughly 0.6 of a monolayer of sulfide which inhibits initial oxidation of the surface. The sulfide is not lost as the surface becomes oxidized but appears to remain near the GaAs/oxide interface. Furthermore, in the oxidized layer, As oxide is preferentially drawn to the surface relative to Ga oxide.

Surface passivation effects of As2S3 glass on self-aligned AlGaAs/GaAs heterojunction bipolar transistors

Abstract: A recently developed As2S3 chemical treatment was used to passivate the perimeters of self‐aligned heterojunction bipolar transistors (HBTs). The As2S3 chemical treatment significantly lowered the base current resulting in a two order of magnitude reduction in the collector current density at which dc current gain was observed (β=1). No degradation with time has been observed in the electrical characteristics of the chemically treated HBTs. This absence of degradation is attributed to the impermeability to oxygen of the As2S3 glass which coats the perimeter of the HBT after chemical treatment.

Effects of perimeter recombination on GaAs-based solar cells

Abstract: Perimeter recombination currents have been experimentally characterized on GaAs p/n heteroface diodes and solar cells with areas ranging from 2.5*10/sup -5/ to 0.25 cm/sup 2/. Under 1-sun operation at the maximum power point, measurements show that the n approximately=2 perimeter recombination current component degrades the cell's fill factors but does not greatly affect the open-circuit voltage. The n approximately=2 perimeter recombination currents are examined theoretically on small-area cells using a two-dimensional drift-diffusion device simulator, PUPHS2D. This model verifies the importance and origin of perimeter recombination in heteroface GaAs-based solar cells. Two methods of reducing the n approximately=2 perimeter recombination are explored. >

Effects of low work function metals on the barrier height of sulfide‐treated n‐type GaAs(100)

Abstract: A comparative study of the Schottky barrier height variation on sulfide‐treated GaAs(100) surfaces with low work function metal contacts was made using current‐voltage and capacitance‐voltage measurements. Five different wet chemical sulfide treatments were found to cause little variation in the Sm (0.72 eV) and Mg (0.59 eV) Schottky barrier heights, but caused significant variation in the Al (0.58–0.75 eV) barrier heights when compared to the untreated control diodes. A low temperature (160 °C) anneal was found to cause variation in all of these, uniformly raising the barrier heights of the Sm (+0.07 eV) and Al (+0.04 eV) contacts, and degrading the Mg contacts. These results demonstrate the critical importance of both the reaction specifics and the stability of the interface on the Schottky barrier height.

Electronic passivation of GaAs surfaces through the formation of arsenic—sulfur bonds

Abstract: X‐ray photoelectron spectroscopy reveals that the remarkable electronic quality of GaAs/sulfide interfaces can be ascribed to the formation of AsxSy phases which grow on an oxide‐free GaAs surface. While one of these phases is akin to As2S3, another shows significant in‐plane S—S bonding. Raman experiments indicate that the band bending on this disulfide‐ terminated surface has been reduced to 0.12 eV.

Chalcogenide passivation of III–V semiconductor surfaces

Abstract: Experimental studies of chalcogenide passivation (by sulfur and selenium atoms) of III–V semiconductor surfaces are analyzed. The characteristic features of chemical-bond formation, the atomic structure, and the electronic properties of III–V semiconductor surfaces coated with chalcogenide atoms are examined. Advances in recent years in the application of chalcogenide passivation in semiconductor technology and trends and prospects for further development of this direction are discussed.

Chemical studies of the passivation of GaAs surface recombination using sulfides and thiols

Abstract: Steady-state photoluminescence, time-resolved photoluminescence, and x-ray photoelectron spectroscopy have been used to study the electrical and chemical properties of GaAs surfaces exposed to inorganic and organic sulfur donors. Despite a wide variation in S2–(aq) concentration, variation of the pH of aqueous HS–solutions had a small effect on the steady-state n-type GaAs photoluminescence intensity, with surfaces exposed to pH=8, 0.1-M HS–(aq) solutions displaying comparable luminescence intensity relative to those treated with pH=14, 1.0-M Na2S·9H2O(aq). Organic thiols (R-SH, where R=–CH2CH2SH or –C6H4Cl) dissolved in nonaqueous solvents were found to effect increases in steady-state luminescence yields and in time-resolved luminescence decay lifetimes of (100)-oriented GaAs. X-ray photoelectron spectroscopy showed that exposure of GaAs surfaces to these organic systems yielded thiols bound to the GaAs surface, but such exposure did not remove excess elemental As and did not form a detectable As2S3 overlayer on the GaAs. These results imply that complete removal of As0 or formation of monolayers of As2S3 is not necessary to effect a reduction in the recombination rate at etched GaAs surfaces. Other compounds that do not contain sulfur but that are strong Lewis bases, such as methoxide ion, also improved the GaAs steady-state photoluminescence intensity. These results demonstrate that a general class of electron-donating reagents can be used to reduce nonradiative recombination at GaAs surfaces, and also imply that prior models focusing on the formation of monolayer coverages of As2S3 and Ga2S3 are not adequate to describe the passivating behavior of this class of reagents. The time-resolved, high level injection experiments clearly demonstrate that a shift in the equilibrium surface Fermi-level energy is not sufficient to explain the luminescence intensity changes, and confirm that HS– and thiol-based reagents induce substantial reductions in the surface recombination velocity through a change in the GaAs surface state recombination rate.

Mechanisms of current flow in metal-semiconductor ohmic contacts

Abstract: Published data on the properties of metal-semiconductor ohmic contacts and mechanisms of current flow in these contacts (thermionic emission, field emission, thermal-field emission, and also current flow through metal shunts) are reviewed. Theoretical dependences of the resistance of an ohmic contact on temperature and the charge-carrier concentration in a semiconductor were compared with experimental data on ohmic contacts to II–VI semiconductors (ZnSe, ZnO), III–V semiconductors (GaN, AlN, InN, GaAs, GaP, InP), Group IV semiconductors (SiC, diamond), and alloys of these semiconductors. In ohmic contacts based on lightly doped semiconductors, the main mechanism of current flow is thermionic emission with the metal-semiconductor potential barrier height equal to 0.1–0.2 eV. In ohmic contacts based on heavily doped semiconductors, the current flow is effected owing to the field emission, while the metal-semiconductor potential barrier height is equal to 0.3–0.5 eV. In alloyed In contacts to GaP and GaN, a mechanism of current flow that is not characteristic of Schottky diodes (current flow through metal shunts formed by deposition of metal atoms onto dislocations or other imperfections in semiconductors) is observed.