Semiconductor components, in particular photodetectors,...

Details Semiconductor components, in particular photodetectors,... Semiconductor components, in particular photodetectors,...

1997-04-08

2002-06-11

Tran, Minh Loan (Department: 2811)

Active solid-state devices (e.g., transistors, solid-state diode

Thin active physical layer which is

Heterojunction

C257S018000, C257S019000, C257S021000, C257S022000, C257S103000

Reexamination Certificate

active

06403975

ABSTRACT:

FIELD OF THE INVENTION
Photodetectors and light emitting diodes (LEDs) in the wavelength range from 1.55 to 1.3 &mgr;m are used in telecommunication by means of glass fibers. At present, use is principally made of components based on III-V semiconductors which are relatively expensive.
DESCRIPTION OF PRIOR ART
Some proposals have been made relating to Si
1-x
Ge
x
/Si semiconductor components for use in this wavelength range and have been reported by H. Presting et al. in Semiconductor Science Technology 7, pages 1127 and sequel of 1992 and in App. Phys. Lett., Vol. 66 No. 17, Apr. 24, 1995 in the article “Strained Si
1-x
Ge
x
multi-quantum well waveguide structure on (110) Si” by K. Bernhard Höfer, A. Zrenner, J. Brunner and G. Abstreiter.
However, substantial problems exist with such Si
1-x
Ge
x
/Si structures because Ge has a lattice constant which differs substantially from that of Si. The mechanical strain which thereby results in structures of this kind makes it necessary to restrict the thickness of the layers to an extent which places severe constraints on the use of the Si
1-x
Ge
x
/Si material system.
Proposals have also been made relating to light emitting diodes, realized by a p-n junction formed in silicon carbide.
That is to say, the junction is formed by the transition from a p-SiC substrate to an n-SiC layer, with the contacts being provided at the two layers. One proposal of this kind is to be found in DE-A-23 45 198. A further discussion of this system is also to be found in DE-A 39 43 232 which states that SiC based LEDs are disadvantageous in comparison with various LEDs based on III-V or II-VI material systems. The reason given is that SiC has the disadvantage that the light yield for a p-n LED is low because SiC is a material with an indirect band gap. The document concludes that SiC LEDs cannot therefore be used for practical applications.
Finally, for the sake of completeness, reference should be made to DE-A-35 36 544 which discusses the deposition of a layer of semiconductor material from the gas phase onto the and of a glass fiber to form a detector. This is intended as a particularly simple way of coupling out the light from the glass fiber while simultaneously converting it into an electrical signal. It is stated that amorphous (hydrogen-containing) Si and amorphous compounds of Si with Ge, carbon or tin, amorphous Si carbide or Si nitride can be used as a semiconductor. This reference is not considered relevant to the present teaching, which is concerned with single crystal material.
OBJECT OF THE INVENTION
The present invention is based on the object of providing semiconductor components in the form of photodetectors, light emitting diodes, optical modulators and waveguides which can be grown on a silicon substrate at favorable cost, which permit adjustment of the effective band gap, which enable a pronounced localization of electrons and holes, which do not require the use of complicated relaxed buffer layers, which bring about enhanced optical absorption and emission and allow these parameters to be influenced and which, in certain structures, permit the optical absorption and emission to be changed (modulated) in energy and amplitude by the application of a voltage.
BRIEF DESCRIPTION OF THE INVENTION
In order to satisfy this object, there is provided a semiconductor component, such as a photodetector, a light emitting diode, an optical modulator or a waveguide formed on an Si substrate, characterized in that the active region consists of a layer structure with Si
1-y
C
y
, Si
1-x
Ge
x
, and/or Si
1-x-y
Ge
x
C
y
alloy layers or a multi-layer structure built up of such layers.
More specifically, the present invention relates to a semiconductor component having any one of the following structures:
a) a single layer of Si
1-y
C
y
b) a superlattice comprising alternating layers of Si and Si
1-y
C
y
c) a superlattice comprising alternating layers of Si
1-y
C
y
and Si
1-x
Ge
x
d) a superlattice comprising alternating layers of Si
1-y
C
y
and Si
1-x-y
Ge
x
C
y
, with the atomic fraction y of the Si
1-x-y
Ge
x
C
y
layers being equal to or different from the atomic fraction y of the Si
1-y
C
y
layers
e) a superlattice comprising a plurality of periods of a three-layer structure comprising Si, Si
1-y
C
y
and Si
1-x
Ge
x
layers
f) a single layer of Si
1-x-y
Ge
x
C
y
g) a superlattice comprising alternating layers of Si and Si
1-x-y
Ge
x
C
y
and
h) a superlattice comprising a plurality of periods of a three-layer structure comprising Si, Si
1-y
C
y
and Si
1-x-y
Ge
x
C
y
layers, with the atomic fraction of y of the Si
1-x-y
Ge
x
C
y
layers being equal to or different from the atomic fraction y of the Si
1-y
C
y
layers.
An important recognition underlying the present invention is namely that Si-based multilayer or superlattice structures with Si
1-y
C
y
/Si
1-x
Ge
x
/and/or Si
1-x-y
Ge
x
C
y
alloy layers open up the possibility of tailoring the lattice constants, the band gap and the shape of the band edges for the various semiconductor components.
In particular it has been found that it is possible to grow both Si
1-x
Ga
x
/Si
1-y
C
y
and Si
1-x-y
Ge
x
C
y
/Si
1-y
C
y
multilayer structures which are nearly compensated in average strain, and which do not suffer from deterioration of their properties due to strain relaxation. It has been found that with multilayer structures with at least double quantum wells, surprising properties are obtained which are considerably enhanced in comparison to the properties obtained with single quantum wells. Thus, for example, an improved photoluminescent efficiency has been found for Si
1-x-y
Ge
x
C
y
/Si
1-y
C
y
double quantum wells embedded in Si when compared to single quantum wells. This enhancement is considered to be quite remarkable considering the small overlap of the charge carrier wave functions. Considerably higher photoluminescent transition rates are achieved with short period Si
1-x-y
Ge
x
C
y
/Si
1-y
C
y
superlattice structures. Further enhanced photoluminescent transitions and an efficient capture of excited carriers even at room temperature can be expected for larger Ge and C contents, which appear to be practicable.
From experiments conducted to data it appears that photoluminescence can be achieved at the wavelengths of particular interest for optical fiber transmissions, i.e. in the range from 1.55 to 1.3 &mgr;m (corresponding to 0.7 to 0.85 eV) and that the efficiencies which can be achieved will competitive with those of existing LEDs based on III-V or II/Vi material systems. Moreover, since the photoluminescent devices proposed here are based on Si, they should be readily acceptable and less expensive to produce, making use of known Si processing technology.
Hitherto the carbon required for the semiconductor components proposed here has been obtained from a graphite filament. It is believed that higher carbon concentrations will be achievable and the process will be better controllable in future. Carbon may also be deposited from the gas phase using suitable carbon-containing gases, such as methane or propane in a chemical vapor deposition system (CVD).
The atomic fractions x of Ge and y of C in the Si
1-x-y
Ge
x
C
y
layers and of y in Si
1-y
C
y
layers may be chosen in accordance with the guidelines given in claims
3
to
6
. The values given there enable the realization of semiconductor components with beneficial properties in the sense of satisfying the objects outlined above.
The Si
1-x-y
Ge
x
C
y
, Si
1-y
C
y
and Si
1-x
Ge
x
layers are all substantially undoped, i.e. if dopants are present, they are due to impurities which cannot be avoided in practice. They are not, however, usually intentionally added to modify the properties of the devices under discussion.
The useful thicknesses of the alloy layers proposed in the present application in multi-layer and superlattice structures has generally been found to lie in the range from about 0.5 nm to about 10 nm.
When realizing the semiconductor components using superlattice structures, which have particularly beneficial prop

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