Active solid-state devices (e.g. – transistors – solid-state diode – Thin active physical layer which is – Heterojunction
Patent
1994-07-22
1996-06-18
Hille, Rolf
Active solid-state devices (e.g., transistors, solid-state diode
Thin active physical layer which is
Heterojunction
257 21, 257 25, 257184, H01L 2906, H01L 310328
Patent
active
055280510
DESCRIPTION:
BRIEF SUMMARY
This invention concerns semiconductor infrared detectors.
These detectors have particularly advantageous applications in the range from 8 .mu.m to 12 .mu.m because these wavelengths correspond to a transparent window in the atmosphere. However, although this is a preferred sensitivity range, the invention is not limited to this particular range of values.
The material used most often for these semiconductor detectors is the alloy HgCdTe but this material is metallurgically extremely complex, which makes its industrial production difficult.
Several laboratories have recently proposed using a new type of infrared detector--of the generic type to which the detector of the invention pertains--based on the principle of absorption of photons associated with transitions between two quantum sub-bands appearing in the quantum wells created by stacking a very large number of alternating epitaxial layers of III-V semiconductor material.
The advantage of these detectors comes mainly from the fact that the use of III-V compounds in place of II-VI compounds such as HgCdTe involves matellurgy that is much more manageable, making it easier to effect industrial production of these detectors.
However, for various reasons which are explained in detail below, the performance of these quantum well detectors with III-V semiconductors has so far been inferior to that of HgCdTe detectors.
One of the objects of the invention is to overcome this limitation, by providing a quantum well detector with III-V semiconductors which has a high detection sensitivity.
To this end, the detector of the invention, which is of the type specified above, i.e. comprising a succession of alternating stacked layers of a III-V semiconductor material with a large forbidden band and a III-V semiconductor material with a small forbidden band with p-doping, defining a quantum well with sub-bands of HH and LH type in the region of the layer comprising the material with a small forbidden band in the valence band diagram of each corresponding heterostructure, is characterized in that the thickness of the material with a small forbidden band is essentially selected in such a manner that only two quantum sub-levels LH.sub.1 and HH.sub.1 appear in the well, and in that the energy difference between these two sub-levels corresponds to the energy of the photons to be detected, and the composition of the material with the large forbidden band is essentially selected in such a manner that the height of the barrier adjacent the quantum well is equal to or greater than the energy of the LH.sub.1 sub-band.
As to the material with a large forbidden band, its thickness is very advantageously so selected that the potential barriers defined by the layers of this material are sufficiently low for the resonant tunnel effect occurring through these barriers of light holes populating the sub-level LH.sub.1 to create for these light holes a state in which the wave function thereof is spread in the assembly of the quantum wells and potential barriers, while that of the heavy holes populating the HH.sub.1 sub-level is localized.
The material of this structure with a large forbidden band is preferably Al.sub.x Ga.sub.1-x As and the material with a small forbidden band GaAs. In this case, the thickness of the material with a small forbidden band lies in the range 1.5 nm to 2.5 nm approx., and the thickness of the material with a large forbidden band is about 8 nm approx. In a variant, the material with the small forbidden band can be In.sub.y Ga.sub.1-y As, with an indium content Y.sub.In.ltoreq. 0.05 approx.
The invention is now explained in more detail, with reference to the accompanying drawings. In all of the figures the same reference numerals designate like parts.
FIG. 1 is a schematic representation of the conduction band of a stack of AlGaAs/GaAs layers.
FIGS. 2a and 2b show the behavior of the conduction band of a prior art structure, respectively when quiescent and when biased, but with the thickness of the layers of GaAs reduced in such a manner that the energy differen
REFERENCES:
Choi et al., "Multiple quantum well 10 .mu.m GaAs/AlGaAs infaraed detector with improved responsivity", Appl. Phys. Lett. 50 (25), Jun. 1987.
Applied Physics Letters, vol. 59, No. 15, 7 Oct. 1991, pp. 1864-1866, "Normal incidence hole intersubband absorption long wavelength . . . ", by B. F. Levine et al.
Applied Physics Letters, vol. 9, 26 Feb. 1990, pp. 851-853, "High sensitivity low dark current 10 .mu.m GaAs quantum well infrared photodetectors", by B. F. Levine et al.
Applied Physics Letters, vol. 50, No. 16, 20 Apr. 1987, pp. 1092-1094, "New 10 .mu.m infrared detector using intersubband absorption in resonant tunneling . . . ", By B. F. Levine et al.
Journal of Applied Physics, vol. 64, No. 3, 1 Aug. 1988, pp. 1591-1593, "Bound-to-extended state absorption GaAs superlattice transport infrared detectors", by B. F. Levine et al.
Journal Of Vacuum Science and Technology, Part B, vol. 10, No. 2, Mar. 1992, pp. 995-997, "Gas source molecular-beam expitaxial growth of normal incidence . . . ", by J. M. Kuo et al.
Hille Rolf
Picogiga Societe Anonyme
Tran Minhloan
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