Active solid-state devices (e.g. – transistors – solid-state diode – Thin active physical layer which is – Heterojunction
Reexamination Certificate
1999-02-26
2001-08-14
Tran, Minh Loan (Department: 2826)
Active solid-state devices (e.g., transistors, solid-state diode
Thin active physical layer which is
Heterojunction
C257S184000, C257S188000, C257S189000, C257S614000
Reexamination Certificate
active
06274882
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to alloys comprising, in addition to at least one heavy element from column III of Mendeleev's periodic table and specifically indium or thallium, at least two elements from group V usable on a monocrystalline substrate, and a generally binary compound of elements from groups III and V to constitute an infrared emission transducer such as a light-emitting diode, or an infrared detector such as a photodiode.
Numerous composite semiconductors have already been proposed for infrared detection. A widely-used material is (Cd, Hg)Te deposited by epitaxial crystal growth on a monocrystalline substrate of (Cd Te) or of (Cd, Zn)Te. These combinations of elements from groups II and VI of the periodic classification suffer from various drawbacks. Their forbidden bands vary very quickly with alloy composition so that it is difficult to make matrices having a large number of pixels that all have the same cutoff wavelength; the crystal lattice has numerous defects, in particular in thermal infrared detectors, thereby generating noise.
Proposals have also been made for various components that associate elements from groups III and V, and in particular:
(In
1−x
Tl
x
) P on an Inp substrate;
(In
1−x
Tl
x
) As on an InAs substrate;
(In
1−x
Tl
x
) Sb on an InSb substrate; and
(In
1−x
Tl
x
) (As
1−y
P
y
) on an InP substrate.
It is also known that most transducers are designed to operate in the 3 micron (&mgr;m) to 5 &mgr;m range (mid infrared) or in the 8 &mgr;m to 12 &mgr;m range (thermal infrared). The above compounds, described in document WO 96/05621 to which reference can be made, do not make it possible simultaneously and to a sufficient extent, to fulfill both of the conditions that are necessary for making transducers with a large number of pixels, i.e. the ability to adapt cutoff wavelengths merely by changing the proportions of the components, and having very few lattice defects when they are made by epitaxial growth on an appropriate substrate.
SUMMARY OF THE INVENTION
An object of the invention is to provide an epitaxially grown semiconductor material making it possible to build a transducer operating in wavelengths that are adjustable, in particular in the 3 &mgr;m-5 &mgr;m band or in the 8 &mgr;m-12 &mgr;m band, having a zinc blende type crystal structure with a lattice constant that corresponds to that of a GaSb or an AlSb microcrsytalline substrate on which the component can be produced by methods that are now well mastered.
To this end, according to an aspect of the invention, there is provided a compound for an infrared transducer constituted by a quaternary alloy (In
1−x
Tl
x
) (As
1−y
Sb
y
) in which 0≦x<1 and 0<y<1.
A transducer is then constituted by a layer of such material grown epitaxially on a substrate which is generally GaSb or AlSb.
Small concentrations of Sb and Tl suffice to obtain forbidden bands E
0
corresponding to the 3 &mgr;m to 5 &mgr;m and the 8 &mgr;m to 12 &mgr;m bands. Because these concentrations are small, the zinc blende crystal structure of In(As,Sb) is conserved so no difficulty is encountered during epitaxial growth when implementing methods close to the well known methods that are used for making epitaxially-grown layers of InAs, InSb and InAs
1−y
Sb
y
ternary alloys. These small concentrations of Tl and Sb lead to a crystal lattice constant having a value that corresponds to that for GaSb or AlSb monocrystals as used for making the substrate for epitaxial growth. Detectors for use in the 8 &mgr;m-12 &mgr;m band must operate at a temperature that is low, generally about 80 K. At this temperature, the cutoff wavelength for the 8 &mgr;m-12 &mgr;m band corresponds substantially to E
0
=0.1 eV; cutoff for the 3 &mgr;m-5 &mgr;m band corresponds substantially to 0.25 eV. The above-defined quaternary alloy which can in some cases be reduced to an InAs
1−y
Sb
y
ternary alloy makes it possible to obtain a lattice constant corresponding to that of such a monocrystalline substrate of GaSb or AlSb.
Given that it is not known at present how to make TlAs monocrystals, the lattice size of the compound can be calculated only approximately by various approaches. All of them make it possible to determine with sufficient accuracy the precise compositions to be used for the quaternary component. In practice, for a detector that is to operate at 80 K, satisfactory results are obtained with components in which the InAs content is largely in the majority. To obtain a lattice size matching with the GaSb or AlSb substrate in the 3 pm to 5 &mgr;m band (E
0
=0.25 eV) and in the 8 &mgr;m to 12 &mgr;m band (E
0
=0.10 eV), the following results have been obtained:
GaSb substrate
band:
3 &mgr;m-5 &mgr;m:
y = 7% to 8%
x = 4% to 5%
(1)
8 &mgr;m-12 &mgr;m:
y = 3% to 6%
x = 12% to 15%
AlSb substrate
3 &mgr;m-5 &mgr;m:
y = 18% to 19%
x = 0%
8 &mgr;m-12 &mgr;m:
y = 14% to 16%
x = 8% to 10%
In practice, infrared transducers are made that comprise a binary substrate supporting an epitaxial (In
1−x
Tl
x
) (As
1−y
Sb
y
) layer in which the values of x and y are much less than 1, and generally less than 0.2.
On top, the transducer may have an n+ doped accumulation layer, while the main layer is of p type; the disposition could be reversed.
The above characteristics and others will appear more clearly on reading the following description of particular embodiments given as non-limiting examples. The description refers to the accompanying drawings:
REFERENCES:
patent: 5462008 (1995-10-01), Razeghi
patent: 5577061 (1996-11-01), Hasenberg et al.
patent: WO 96/05621 (1996-02-01), None
patent: 9605621 (1996-02-01), None
Asahii et al.; “New semiconductors T1InGaP and their gas source MBE growth”; Proceedings of the Ninth International Conference on Molecular Beam Epitaxy, Malibu, CA, USA, Aug. 5-9, 1996, vol. 175-1762, pp. 1195-1199. XP002081274—ISSN 0022-0248, Journal of Crystal Growth, May 1997, Elsevier, Netherlands—Whole document.
Patent Abstracts of Japan—vol. 007, No. 049 (E6161), Feb. 25, 1983 & JP 197877 A (Nippon Denki KK), Dec. 4, 1982 Abstract.
Lorans Dominique
Poirier Michel
Verie Christian
Larson & Taylor PLC
Sagem SA
Tran Minh Loan
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