R. W. Grant

Metal Schottky barrier contacts to alpha 6H:SiC

Formation of Schottky barrier contacts to n‐type 6H‐SiC for a number of metals chosen to include a variety of physical and chemical properties has been investigated. The metals (Pd, Au, Ag, Tb, Er, Mn, Al, and Mg) were deposited onto room temperature surfaces terminated with a submonolayer coverage of oxygen. The metal/6H‐SiC interface chemistry and Schottky barrier height φB during contact formation were obtained with x‐ray photoemission spectroscopy; the electrical properties of subsequently formed thick contacts were characterized by current‐voltage and capacitance‐voltage techniques. The o/B values for these metals extend over a wide 1.3 eV range. To a varying degree φB depends on the 6H‐SiC crystal face (Si vs C). Mg and Al (Si face of latter) have φB=0.3 eV, a value which is suitable for nonalloyed ohmic contacts.

Schottky barrier height and interface chemistry of annealed metal contacts to alpha 6H‐SiC: Crystal face dependence

The electrical properties and interface chemistry of unannealed and annealed Ni, Ti, and Al contacts to both Si (0001) and C (0001) terminated faces of 6H‐SiC are compared by using x‐ray photoemission spectroscopy, current‐voltage, and capacitance‐voltage data. For annealing temperatures in the 400 to 600 °C range Ni and Ti contacts have significantly more dissociation of interface SiC and formation of reaction products for the C‐face than the Si‐face. The chemical reactivity of the Al contact was limited and equal for both faces. Stability of the Schottky barrier height with annealing, which has a wide variation according to metal and face, is not correlated with the degree of metal/6H‐SiC interface chemical reactivity

Nucleation and strain relaxation at the InAs/GaAs(100) heterojunction

The techniques of molecular beam epitaxy have been used to investigate the nucleation and growth of InAs heteroepitaxial thin films lattice mismatched to GaAs(100) substrates. Our previous observations have been that optimum structural and electrical properties are obtained only if the heteroepitaxial nucleation sequence is carried out under experimental conditions leading to the indium stabilized (4×2) InAs(100) surface reconstruction. In this work, reflection electron diffraction, Auger electron spectroscopy and x‐ray diffraction have been used to determine the InAs(100) surface phase diagram. The InAs/GaAs(100) heterojunction grown by MBE is abrupt and smooth surfaces are obtained only under indium stabilized nucleation conditions. A residual compressive strain at the crystalline interface occurs which is somewhat relieved by a tetragonal distortion in the direction normal to the film plane. Results of investigations by reflection electron diffraction show that the nucleation of InAs/GaAs(100) occurs v...

Formation and Schottky barrier height of metal contacts to β‐SiC

Formation of Schottky barrier contacts to n‐type β‐SiC(100) was systematically investigated for several metals with various physical and chemical properties. The metals (Pd, Au, Co, Ti, Ag, Tb, and Al) were deposited onto oxygen terminated (∼1 monolayer) surfaces. Metal/β‐SiC interface chemistry and Schottky barrier height φB during contact formation were obtained by x‐ray photoemission spectroscopy; the corresponding electrical properties of thick contacts were characterized by capacitance‐voltage and current‐voltage methods. The metal/β‐SiC interface is unreactive at room temperature. X‐ray photoemission spectroscopy and electrical measurements demonstrate that these metal contacts exhibit a wide range of φB , 0.95–0.16 eV; within this range an individual contact φB value depends strongly on the metal work function in general accord with the Schottky–Mott limit.

Measurement of InP/In0.53Ga0.47As and In0.53Ga0.47As/In0.52Al0.48As heterojunction band offsets by x‐ray photoemission spectroscopy

X‐ray photoemission spectroscopy (XPS) has been used to measure the valence‐band offset ΔEv for the lattice‐matched InP/ In0.53Ga0.47As and In0.53Ga0.47As/ In0.52Al0.48As heterojunction interfaces. The heterojunctions were formed by molecular‐beam epitaxy. We obtain values of ΔEv (InP/In0.53Ga0.47As) =0.34 eV (ΔEc/ ΔEv=43/57) and ΔEv (In0.53Ga0.47As/ In0.52Al0.48As) =0.22 eV (ΔEc/ ΔEv =68/32) for the respective interfaces. By combining these measurements with available XPS ΔEv (InP/ In0.52Al0.48As) data we find that band offset transitivity is satisfied. Accordingly, the band offsets for heterojunction pairs formed from InP, In0.53Ga0.47As, and In0.52Al0.48As are not influenced by interface specific effects.

Study of interface asymmetry in InAs–GaSb heterojunctions

We present reflection high energy electron diffraction, secondary ion mass spectroscopy, scanning tunneling microscopy and x‐ray photoelectron spectroscopy studies of the abruptness of InAs–GaSb interfaces. We find that the interface abruptness depends on growth order: InAs grown on GaSb is extended, while GaSb grown on InAs is more abrupt. We first present observations of the interfacial asymmetry, including measurements of band alignments as a function of growth order. We then examine more detailed studies of the InAs–GaSb interface to determine the mechanisms causing the extended interface. Our results show that Sb incorporation into the InAs overlayer and As exchange for Sb in the GaSb underlayer are the most likely causes of the interfacial asymmetry.

Metal contacts to GaAs with 1 eV Schottky barrier height

Metal Schottky barrier contacts to n‐type (100) GaAs are described in which a 1 eV Schottky barrier height φB is achieved by using a very thin Si interface layer to influence the interface Fermi energy EiF. The metals investigated are Au, Cr, and Ti. The contact structure consists of a thick metal in combination with a ∼15–30 A heavily p‐type Si interface layer. The EiF and interface composition during initial contact formation were obtained by x‐ray photoemission spectroscopy (XPS); the φB for the corresponding thick contacts was measured by current‐voltage (I‐V) and capacitance‐voltage (C‐V) techniques. The XPS, I‐V, and C‐V measurements gave consistent results. The 1 eV φB for the Si interface layer contact structure is independent of the contact metal.

Correlation of interface composition and barrier height for model AuGeNi contacts to GaAs

Model contacts to GaAs that include nonalloyed layered structures of Au, Ge, and Ni in various combinations are used to establish a correlation between interface composition and large changes in barrier height φB. The interface Fermi level EiF and chemistry during initial contact formation were investigated by x‐ray photoemission spectroscopy; the corresponding φB for the thick contact was obtained by current‐voltage (I‐V) measurement. The circumstances under which a thin (∼10 A) Ge layer at the GaAs interface can produce φB =∼0.25–0.4 eV (as measured by I‐V) are described. For all model contacts examined a φB range from ∼0.25 to 0.9 eV is observed. This result questions the usual assumption of a relatively fixed φB of ∼0.8 eV for the alloyed AuGeNi contact and offers an alternative explanation for the mechanism of ohmic contact formation. The conditions that define the exceptionally low φB contacts provide a guide for the design of nonalloyed tunnel ohmic contacts.

Measurement of potential at semiconductor interfaces by electron spectroscopy

Electron spectroscopy performed in ultrahigh vacuum can be used to measure potential and heterojunction band discontinuities at abrupt semiconductor interfaces. The technique provides a direct contactless and nondestructive means to determine and correlate interface chemistry and potential. This article discusses some of the factors which affect applications of Auger electron spectroscopy, ultraviolet photoelectron spectroscopy, soft x‐ray photoelectron spectroscopy, and x‐ray photoelectron spectroscopy for semiconductor interface potential measurements.

Correlation of Fermi‐level energy and chemistry at InP(100) interfaces

X‐ray photoemission spectroscopy data are used to correlate the interface Fermi‐level pinning energy EiF and the corresponding interface chemistry for n‐type and p‐type InP (100) samples simultaneously subjected to a series of surface treatments. Interfaces of Schottky‐barrier contacts formed during a sequence of Au and of Al depositions made both onto chemically etched and thermally cleaned InP surfaces were investigated. Changes in EiF of up to ∼0.6 eV in the upper half of the InP band gap occurred in response to changes in interface chemistry. The observed behavior of EiF is interpreted in terms of a single defect model with multiple charge states.