Classifications

• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
  • H01L31/00—Semiconductor devices sensitive to infrared radiation, light, electromagnetic radiation of shorter wavelength or corpuscular radiation and specially adapted either for the conversion of the energy of such radiation into electrical energy or for the control of electrical energy by such radiation; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof
  • H01L31/0248—Semiconductor devices sensitive to infrared radiation, light, electromagnetic radiation of shorter wavelength or corpuscular radiation and specially adapted either for the conversion of the energy of such radiation into electrical energy or for the control of electrical energy by such radiation; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof characterised by their semiconductor bodies
  • H01L31/0352—Semiconductor devices sensitive to infrared radiation, light, electromagnetic radiation of shorter wavelength or corpuscular radiation and specially adapted either for the conversion of the energy of such radiation into electrical energy or for the control of electrical energy by such radiation; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof characterised by their semiconductor bodies characterised by their shape or by the shapes, relative sizes or disposition of the semiconductor regions
  • H01L31/035236—Superlattices; Multiple quantum well structures
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B82—NANOTECHNOLOGY
  • B82Y—SPECIFIC USES OR APPLICATIONS OF NANOSTRUCTURES; MEASUREMENT OR ANALYSIS OF NANOSTRUCTURES; MANUFACTURE OR TREATMENT OF NANOSTRUCTURES
  • B82Y20/00—Nanooptics, e.g. quantum optics or photonic crystals

Definitions

• the invention relates to infrared semiconductor detectors.
• these detectors find particularly interesting applications, since these wavelengths correspond to a window of atmospheric transparency.
• the invention is not limited to this particular range of values.
• the material used for these semiconductor detectors is the HgCdTe alloy, but this material is of extremely complicated metallurgy, which makes its industrial production difficult.
• One of the aims of the invention is to overcome this limitation, by proposing a quantum well detector on III-V semiconductors which has high detectivity.
• the detector of the invention which is of the aforementioned type, that is to say comprising a succession of alternating stacked layers of III-V semiconductor material with large forbidden band and of a p-doped small band LII-V semiconductor material defining in the valence band diagram of each corresponding heterostructure, at the level of the layer comprising the material with small band gap, a quantum well comprising sub-bands of Type HH and LH, is characterized in that the ceremoni ⁇ sor of the small band gap material is essentially so selected that do not appear in the wells as two sublevels quantum ⁇ LH and HH] ⁇ , and that the difference of energy between these two sub-levels corresponds to the energy of the photons to be detected, and the composition of the material with a large forbidden band is essentially chosen so that the barrier height of the quantum well is equal to or greater than the energy of the liK- ⁇ sub-band.
• the material with a large forbidden band its thickness is very advantageously chosen so that the width of the potential barriers defined by the layers of this material are sufficiently small so that the tunnel effect resonating through these barriers, light holes populating the sub-level ⁇ creates for these light holes a state where the wave function of these latter is delocalized over all of the quantum wells and potential barriers, while that of the heavy holes populating the sub-level HH 1 is localized.
• the material with a large band gap of this structure is preferably Al ⁇ -Ga ⁇ As and the material with a small band gap, GaAs.
• the thickness of the material with a small prohibited band is between 1.5 and 2.5 nm approximately and the thickness of the material with a large prohibited band is of the order of 8 nm. about.
• the material with a small forbidden band can be LL.Ga 1 _ ⁇ As, with an indium y In content of ⁇ 0.05 approximately.
• Figure 1 is a schematic representation of the strip of conduction of a stack of AlGaAs / GaAs layers.
• FIGS. 2a and 2b illustrate, respectively at rest and under polarization, the shape of the conduction band of a structure of the prior art, but the thickness of the layers of GaAs of which has been reduced so that the difference d energy of the quantum sub-bands corresponds to the wavelength of the light to be detected.
• FIGS. 3a and 3b are homologous to FIGS. 2a and 2b, in the case where the composition of the layer of AlGaAs has been chosen so that the upper quantum sub-level is flush with the edge of the quantum well.
• Figure 4 is a schematic representation of the valence band of a stack of AlGaAs / GaAs layers.
• FIGS. 5a and 5b illustrate, respectively at rest and under polarization, the shape of the valence band of a structure of the prior art such as that of FIG. 4.
• Figures 6a and 6b are homologous to Figures 5a and 5b, but for a structure whose doping and sizing of the layers have been determined in accordance with the teachings of the invention.
• Figures 7a and 7b are homologous to Figures 6a and 6b, for a variant implementation of the invention.
• these detectors consist, as illustrated in FIG. 1, of a stack of heterostructures 1 each formed by a layer 2 of GaAs and a layer 3 of AlGaAs. These different layers are epitaxial on each other, and the complete stack can comprise up to fifty heterostructures 1.
• This configuration of layers creates in the conduction band E shown schematically in FIG. 1 a corresponding succession te of discontinuities alternating quantum wells 4 and potential barriers 5.
• the GaAs layers are sufficiently thin, of the order of a few nanometers, it appears by quantum effect quantum subbands (quantum levels) E 1 ⁇ E 2 , E 3 , etc.
• quantum effect quantum subbands quantum levels
• the thickness of the GaAs layers that is to say of the width of the quantum wells 4
• the first detectors produced according to this principle were described by BF Levine et al., New 10 ⁇ m Infrared Detector Using Intersubband Absorption in Resonant Tunneling GaAIAs Superlattices, Appl. Phys. Lett., Vol. 50, No. 16, p. 1092 (1987). We then ren ⁇ of the account of the incidence of a parasitic tunnel current due to the electrons of the level ⁇ whose tunnel transparency, although weaker than that of the electrons of the level E 2 , cannot be neglected. This tunnel current thus creates a high dark current, detrimental to the performance of the detector.
• ⁇ E the barrier height for the electron concerned (A ⁇ l for the sub-band ⁇ - and ⁇ E 2 for sub-band E 2 ), d being the thickness of the potential barrier of AlGaAs, and
• V being the applied voltage
• a first limitation of the performance of this structure is due to the short lifetime of the electrons in the structure, which is linked to the lifetime of the electrons in the material (AlGaAs) constituting the potential barrier in which the hot electrons move.
• a second limitation is probably due to the phenomenon of inter-sub-band optical absorption, which must obey certain rules of selection of quantum mechanics preventing the incident light from being perpendicular to the plane of the layers.
• Figures 5a and 5b schematically represent the case described by Levine in the last aforementioned article: these are quanti ⁇ cal wells 9 3 to 4 nm wide, with a barrier height ⁇ E V of the order of 160 mV , for an aluminum content of 0.30 of the AlGaAs material (here and below, the term “content” will be understood to mean the molar fraction ⁇ j of Al x Ga 1 _ x As).
• the HH 2 sub-band is practically at the edge of the quantum well and the energy difference between the edge of the well and the HH 1 sub-band is 144 mV for a 3 nm well, or 157 mV for a 4 nm well ( Figure 5a).
• This structure of the prior art also has the disadvantage of the presence, in the quantum wells 9, of the sub-band. LH ⁇ . Indeed, this sub-band is populated with holes of low effective mass and which are located approximately 50 mV from the edge of the quanti ⁇ well. If we consider equation (1) above, the tunnel transparency of these light holes is therefore high, all the more so as the Fermi level approaches LH 1 level ( i.e. - say that the layer of
• GaAs is p-doped - which is the case here, with dopings of between 10 17 and 5.10 18 cm “3 approximately.
• dopings between 10 17 and 5.10 18 cm “3 approximately.
• the invention which will now be described, aims precisely to overcome this difficulty. His lessons lie mainly in an appropriate choice of the composition of the AlGaAs alloy and the thicknesses of the GaAs and AlGaAs layers.
• the invention uses in particular the phenomenon of inter-subband transition HH-L and LH- ⁇ to eliminate, firstly, the parasitic tunnel effect due to the light holes LH ⁇
• the width of the AlGaAs barrier may be reduced as necessary since the holes populating the sub-level ⁇ L ⁇ .- ⁇ are heavy holes, having a low tunnel transparency and therefore having only low impact on detector performance.
• the energy difference between the two sub-bands LH- and ⁇ must be obtained. 1 is of the order of 124 mV. Calculations of quantum mechanics make it possible to establish that, in this case, the width of the well must be of the order of 1.5 to 2.5 nm, this thickness depending on the height of the potential barrier, c that is, the aluminum content of AlGaAs. The calculation shows that the barrier height ⁇ E V must exceed approximately 230 mV, which imposes an aluminum content greater than approximately 0.42.
• FIG. 6a at equilibrium
• 6b under illumination and under electric field
• the quantum well detector of the invention is thus constituted by a succession of quantum wells 9 of very small width (about 1.5 to 2.5 nm), separated by potential barriers 10 which are themselves relatively thin.
• barrier heights such that the LH-L sub-band is located just at the edge of the quantum well, as illustrated in FIGS. 7a and 7b ; in this case, the barrier height ⁇ E V of the quantum well is no longer greater, but just equal to the energy of the sub-band LH L.
• This configuration is close to that presented in FIGS. 5a and 5b (corresponding to Levine's proposal in the aforementioned article) but it has the essential difference of the presence, in the situation of the prior art, of the sub -bandaged LH- s ⁇ ue in the quantum well below the potential barrier, thus contributing to increasing the dark current.
• the holes populating the HH ⁇ sub-band which not only have a large effective mass but which, moreover, are located deep in the well, they do not undergo a tunnel effect and their wave function also remains localized.
• the light holes LH 2 moving in the periodic potential have a longer lifespan than the heavy holes moving in the continuum of the valence band, as explained above with reference to FIG. 5.
• the displacement of the holes of the LH-L strip is favored by a small barrier width (a small thickness of AlGaAs layer)
• MOCVD metal-organic chemical vapor deposition
• the invention is not restricted to a GaAs / ALGaAs heterojunction, its teachings also being able to apply to other heterostructures formed from HI-V alloys.
• the InGaAs alloy can be used in place of GaAs to produce the quantum wells.
• this alloy InGaAs being of larger mesh parameter than GaAs, it will undergo a uniaxial stress which will have the effect of repelling the sub-band LH-L P ⁇ US ⁇ OU1 in energy, in other words increasing the difference of energy between the sub-bands HH 1 and LH-L. - ⁇
• this Phenomenon it is possible, for equal performances, to widen the quantum well compared to a similar structure using GaAs, and therefore to facilitate practical realization thanks to a less thinness of the layer to be deposited.

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• 1992
  • 1992-01-22 FR FR9200667A patent/FR2686456A1/fr active Pending
• 1993
  • 1993-01-21 EP EP93904105A patent/EP0623245A1/de not_active Withdrawn
  • 1993-01-21 JP JP5512971A patent/JPH07506460A/ja active Pending
  • 1993-01-21 WO PCT/FR1993/000060 patent/WO1993015525A1/fr not_active Application Discontinuation
  • 1993-01-21 US US08/256,760 patent/US5528051A/en not_active Expired - Fee Related

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