Microstructure and conductance-slope of InAs/GaSb tunnel diodes

Journal Article · Sat Jun 21 00:00:00 EDT 2014 · Journal of Applied Physics

DOI:https://doi.org/10.1063/1.4883756· OSTI ID:22304027

Fitzgerald, Eugene A. ^[1]

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1. Department of Materials Science and Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139 (United States)

InAs/GaSb and similar materials systems have generated great interest as a heterojunction for tunnel field effect transistors (TFETs) due to favorable band alignment. However, little is currently understood about how such TFETs are affected by materials defects and nonidealities. We present measurements of the conductance slope for various InAs/GaSb heterojunctions via two-terminal electrical measurements, which removes three-terminal parasitics and enables direct study on the effect of microstructure on tunnelling. Using this, we can predict how subthreshold swings in TFETs can depend on microstructure. We also demonstrate growth and electrical characterization for structures grown by metalorganic chemical vapor deposition (MOCVD)—a generally more scalable process compared with molecular beam epitaxy (MBE). We determine that misfit dislocations and point defects near the interface can lead to energy states in the band-gap and local band bending that result in trap-assisted leakage routes and nonuniform band alignment across the junction area that lower the steepness of the conductance slope. Despite the small lattice mismatch, misfit dislocations still form in InAs on GaSb due to relaxation as a result of large strain from intermixed compositions. This can be circumvented by growing GaSb on InAs, straining the GaSb underlayer, or lowering the InAs growth temperature in the region of the interface. The conductance slope can also be improved by annealing the samples at higher temperatures, which we believe acts to annihilate point defects and average out major fluctuations in band alignment across the interface. Using a combination of these techniques, we can greatly improve the steepness of the conductance slope which could result in steeper subthreshold swings in TFETs in the future.

• OSTI ID: 22304027
• Journal Information: Journal of Applied Physics, Vol. 115, Issue 23; Other Information: (c) 2014 AIP Publishing LLC; Country of input: International Atomic Energy Agency (IAEA); ISSN 0021-8979
• Country of Publication: United States
• Language: English

Related Subjects

75 CONDENSED MATTER PHYSICS
SUPERCONDUCTIVITY AND SUPERFLUIDITY
ANNEALING
CHEMICAL VAPOR DEPOSITION
CRYSTAL DEFECTS
CURRENTS
DISLOCATIONS
ELECTRIC CONTACTS
FIELD EFFECT TRANSISTORS
GALLIUM ANTIMONIDES
HETEROJUNCTIONS
INDIUM ARSENIDES
INTERFACES
MICROSTRUCTURE
MOLECULAR BEAM EPITAXY
POINT DEFECTS
RELAXATION
STRAINS
TRAPS
TUNNEL DIODES
TUNNEL EFFECT