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Introduction:
The online MOVPE growth database can be found here.
Please note that this is only available from within the physics network.
A major project, funded by the EPSRC, the (Engineering and Physical Research Council)
was run in Oxford from 1985-2004 into the growth of Antimonide structures This had the objectives to:
Develop the growth of thin layers of III-V materials by MOCVD and
Study the physics of low dimensional structures incorporating these layers
The project has covered a variety of different properties for this materials system such as:
Electrical properties:
Two-Dimensional (2D) systems based on GaSb (for example (Ga,In)Sb quantum wells)
allow the investigation of 2D hole gases. Structures based on InAs/(Ga,In)Sb allow
the particularly interesting study of complex bipolar transport involving both 2D electrons
and 2D holes.
Optical Properties:
InAs/(Ga,In)Sb superlattices are the basis of 5-10um detectors using III-V semiconductors.
InSb, In(As,Sb), and InAs/In(As,Sb) superlattices are further candidates in this region of
the infra-red spectrum. The 1.75um band gap of GaSb could lead to structures based on GaSb
with applications in the 1.2-1.7um region with is associated with fiber optic devices.
GaSb/(Ga,In)Sb structures can extend this range to about 3um.
Highlights:
A very large number of layers were grown, with quite a number of these still available for study.
The materials produced are listed on the MOVPE growth database which gives some of the sample details.
We were the first group anywhere to develop the capability to grow these systems using MOVPE.
The InAs/GaSb system has spatially separated, two-dimensional, adjacent layers of electrons [in the InAs]
and holes [in the GaSb]. As a result carrier concentrations can be varied between zero and those characteristic
of very heavily doped semiconductors without the intentional introduction of donors or acceptors, by simply
varying the thickness of the constituent binaries. Since InAs and GaSb share neither a common cation or
anion, an ideal interface can be grown as either a monolayer of GaAs or InSb. Our results can be summarised as follows:
The growth of InAs/GaSb SLSs on the [111] surface leading to enhanced infrared absorption due
to the piezoelectric field increasing the band overlap.
The growth of both GaAs and InSb interfaces in HETs and SLSs. The interfaces controlled by
in-situ monitoring of the alkyls and growth surface by optical absorption.
The observation of optical interface modes in the Raman spectra of SLSs which show the near
perfection of the GaAs and InSb interfaces. TEM measurements confirm monolayer abruptness at the interfaces.
The ability to uniquely distinguish, by means of polarised Raman measurements, the "top"
[GaSb/InAs] from the "bottom" [InAs/GaSb] optical interface modes [whether GaAs or InSb] in SLSs.
The observation [using magnetic field to 50T at He3 temperatures and high pressures] of
different band overlaps (160meV for InSb interfaces and 125meV for GaAs interfaces) and of
interband resonant tunnelling properties which are controlled by the GaAs or InSb interface in HETs.
The fabrication of infrared detectors and emitters, based on short period InAs/GaSb and
InGaSb/GaSb SLSs with band gaps varying between 2 and 20um.
The supression of extrinsic carriers by controlling the interfaces, leading to electron
and hole concentrations within 5% of each other, achieved in no other laboratory in the world.
The first gating of a p-GaSb surface, leading to pinch off for both positive and negative
gate voltages of the carriers in a HET with quantized conductance plateaux for a positive
gate voltage.
Observation of a zero Hall resistance state which occurs when equal numbers of electron and
hole magnetic Landau levels are occupied.
Observation of giant oscillations of the Hall voltage with magnetic field, in strong contrast
to unipolar systems where a monotonic increase occurs and the well known quantized plateaux are observed.
Development of novel Thermal PhotoVoltaic device structures (TPV's)
Observation of new superlattice conduction processes such as Stark and Superlattice magnetophonon effects.
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