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.

Mechanisms of current flow in metal-semiconductor ohmic contacts

We present low-resistive electrical contacts to n-type GaSb with Te doping of 5 × 1017 cm−3 using a Ti/Pt/Au (1/35/275 nm) metalization sequence and an intermediate InAsSb contact layer with n-doping of 1 × 1020 cm−3 (also Te). The high doping level is achieved during growth, so in-diffusion of dopants is not required. To reduce the impact of the native oxide layer we remove it in a sputter-etching process using Ar ions and afterwards deposit the metalization in the same chamber. No annealing is necessary to achieve ohmic IV-characteristics with a resistivity as low as 5.1 × 10−6 Ω cm2. It improves to 3.3 × 10−6 Ω cm2 after annealing at 350 °C for 90 s. The resistivity slightly increases for deeper etching of the native oxide, which is probably due to surface damage induced during the sputter-etching process.

https://iopscience.iop.org/article/10.1088/0268-1242/21/9/011/pdf

Low-resistive metal/n+-InAsSb /n-GaSb contacts

An investigation with the objective of improving n-type ohmic contacts to GaSb-based devices is described. This study involves a series of n-GaInAsSb and n-GaSb samples with varying doping, grown on semi-insulating (SI) GaAs substrates. These samples were fabricated into mesa-etched, transfer-length method (TLM) structures, and the specific-contact resistivity and sheet resistance of these layers as a function of majority electron concentration were measured. Extremely low specific-contact resistivities of about 2 × 10−6 Ω-cm2 and sheet resistances of about 4 Ω/▭ are found for n-type GaInAsSb doped at about 3 × 1018 cm−3.

Ohmic contacts to n-type GaSb and n-type GalnAsSb

Ultra low resistance ohmic contacts are fabricated on n-GaSb grown by molecular beam epitaxy. Different doping concentrations and n-GaSb thicknesses are studied to understand the tunneling transport mechanism between the metal contacts and the semiconductor. Different contact metallization and anneal process windows are investigated to achieve optimal penetration depth of Au in GaSb for low resistances. The fabrication, electrical characterization, and microstructure analysis of the metal-semiconductor interfaces created during ohmic contact formation are discussed. The characterization techniques include cross-sectional transmission electron microscopy and energy dispersive spectroscopy. Specific transfer resistances down to 0.1 Ω mm and specific contact resistances of 1 × 10−6 Ω cm2 are observed.

Electrical and microstructure analysis of nickel-based low-resistance ohmic contacts to n-GaSb

Controlled n-type doping of antimonides and arsenides using GaTe

The quest for faster electronic devices combined with the requirement of low power dissipation has revived the interest in the near 6.1 /spl Aring/ lattice constant antimony containing III-V compounds. Among the known III-V semiconductors, InSb has the highest electron mobility and GaSb the highest hole mobility. In addition favorable bandgap alignments are predicted with related III-V ternaries and quaternaries suitable for high-speed heterostructure transistors, lasers, and optoelectronic devices. The device fabrication technology of antimony containing III-V compounds however, is in its infancy and considerable work needs to be performed. In this work, we report the development of a low contact resistance ohmic contacts for n-type GaSb suitable for heterostructure device applications, with over an order of magnitude improvement in contact resistance and specific contact resistivity. The MBE growth of Te doped n-type GaSb and crucial device processing and pre-metallization surface treatment will be discussed. A variety of metallization schemes containing Au, Ge, In, Ni, Pd, and Pt and the effects of annealing temperature are examined.

Metallization options and annealing temperatures for low contact resistance ohmic contacts to n-type GaSb

In this paper we report on the development of an npn double bipolar transistor with an InGaSb base and InAlAsSb alloys for the emitter and collector. The combination of alloys with a lattice constant of 6.2 a is illustrated. Silvaco simulation indicate that large collector currents, I/sub c/, are possible with this system at smaller base emitter voltages, V/sub BE/, than are measured in the InP based HBT. An important advantage of this system is that the conduction band offset between the InGaSb base and the InAlAsSb may be tuned over a large range while maintaining large valence band offsets that are useful for minimizing parasitic base currents.

InAlAsSb/InGaSb double heterojunction bipolar transistor

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Metallization options and annealing temperatures for low contact resistance ohmic contacts to n-type GaSb

InAlAsSb/InGaSb double heterojunction bipolar transistor