Photodetector-based semiconductor structures with quantum wells

 

(57) Abstract:

Usage: the invention relates to optoelectronics and can be used to create photo-detectors based on epitaxial GaAs/AlxGa1-xAs sensitive to IR-radiation. The essence of the invention: in the photodetector on the basis of semiconductor structures with quantum wells, comprising a substrate of semi-insulating GaAs buffer layer 1 - GaAs first contact layer of N - GaAs, a system of alternating layers of AlxGa1-xAs and GaAs, and in one of the materials system of alternating layers of introduced impurity silicon to the doping level of 21018cm-3and a second contact layer of n - GaAs, silicon is introduced into the layer of AlxGa1-xAs in the form of a monatomic layer, located at a distance not larger Debye length shielded from one boundary of alternating layers. 3 Il.

The invention relates to optoelectronics and can be used to create high-performance photodetectors based on epitaxial GaAs/AlxGa1-xAs sensitive to IR-radiation in the Windows of the atmospheric transmittance in the wavelength range =4-14 microns.

Known photodetectors that are sensitive to Wed"ptx2">

So, for example, photodetectors based ternary compounds CDxHg1-xTe have a maximum sensitivity at =4,5 mm, the photodetectors on the basis of InSb - =3-5 µm [1].

The closest technical solution to the stated photodetector is based on semiconductor structures with quantum wells, comprising a substrate of semi-insulating GaAs buffer layer, an i-GaAs first contact layer of n-GaAs, a system of alternating layers of AlxGa1-xAs and GaAs, and in one of the materials system of alternating layers of introduced impurity silicon to the doping level of 2 1018cm-3and the second contact layer n-GaAs [2]. The mole fraction x of Al in the triple connection is constant and equal to 0.31 in. The doping level of Si in GaAs is 2 to 1018cm-3. Superlattice contains 50 layers each connection (the periodicity of the lattice is equal to 50). Layers of GaAs separated by a wide gap layers of AlxGa1-xAs. E state of n in GaAs localized in the quantum wells. The energy levels of Si in the adjacent GaAs layers do not overlap due to the large thickness of the AlxGa1-xAs. At the border of layers of GaAs and AlxGa1-xAs occurs heterojunctions.

A system of alternating layers with a large difference between their thicknesses can be charact out comparable thickness.

Known photodetector operates as follows. Radiation with energy = hw equal to the value of the energy gap between the levels En in GaAs and area free conditions, provides the transfer of the first electron in this area, and if you have an external pull field E (causing the slope of the band energy diagram) there is an effect of photoconductivity, the value of G is determined by the expression

G= n l V_ , where n is the concentration of photoexcited electrons; V_ - rate; e is the electron charge.

Known photodetector has the following disadvantages.

In the state of thermodynamic equilibrium, the electrons are redistributed between the impurity levels in silicon << Si ->> and the level of n in the potential well in GaAs. Thermal excitation of electrons from the level << Si ->> on level n (process II) and their reverse recombination (process III) lead to the fact that the level n is not fully populated. The latter circumstance limits the quantum yield and reduces the effect of photoconductivity, as not all of the electrons are excited quanta hw (process I), in free zone (Fig. 3 is shaded).

Another disadvantage of the known photodetector is the presence of dark current (with prajda and reduced dark current.

The aim is achieved in that the photodetector on the basis of semiconductor structures with quantum wells, comprising a substrate of semi-insulating GaAs buffer layer, an i-GaAs first contact layer of n-GaAs, a system of alternating layers of AlxGa1-xAs and GaAs, and in one of the materials system of alternating layers of introduced impurity silicon to the doping level of 2 1018cm-3and a second contact layer of n-GaAs, silicon is introduced into the layer of AlxGa1-xAs in the form of a monatomic layer, located at a distance not larger Debye length shielded from one boundary of alternating layers.

The invention consists in the following. Implementation in the quantum barrier layer of wide bandgap material layer dopant causes the electrons from the potential well (Si) becomes energetically advantageous to move to level n in the quantum well layer of GaAs. The reverse process because of the significant energy barrier is difficult. This increases the population level1and, accordingly, the quantum yield.

Because in the field of localization of electrons no impurity States, the proposed photodetector is characterized by the absence of Ki L Lscreenwhere Lscreen- Debye screening length in AlxGa1-xAs. This helps to ensure a smooth transition of electrons from levels in quantum well quantum hole in the GaAs layer.

In Fig. 1 shows schematically the proposed photodetector of Fig. 2, 3 shows the band diagram, respectively, of the inventive photodetector and prototype.

The photodetector is a substrate of semi-insulating GaAs 1 on which is formed a buffer layer, an i-GaAs 2, the first contact layer n-GaAs 3, superlattice, consisting of groups 4 alternating layers of doped silicon i-AlxGa1-xAs 5 and undoped i-GaAs 6, and the second contact layer n-GaAs 7.

The mole fraction x of Al in the triple connection is selected equal to 0.28.

The photodetector grown by molecular-beam epitaxy.

In growth chamber molecular beam epitaxy were placed substrate of semi-insulating GaAs. Then on its surface, purified from impurities (C,O2), has formed a buffer layer, an i-GaAs with a thickness of 1 μm. On top of the buffer layer was increased first contact layer of n-GaAs with a thickness of 1 μm. Next formed a superlattice: layer i-AlxGa1-xAs with x=0.28 and the thickness of the layer 300 and the i-GaAs the dopant - silicon with a concentration of 2 to 1018cm-1.

The operation was repeated to grow at least 10 groups of layers. On the last layer superlattice formed of the second (upper) contact layer of n-GaAs with a thickness of 200 .

The layer thicknesses of the i-GaAs i-AlxGa1-xAs in the superlattice were chosen so that they significantly differed in thickness. This ensures the existence in GaAs quantum wells for electrons and connects the overlap of the wave functions of electrons in adjacent quantum wells.

The combination of the molar fraction of x in the triple connection is 0.28, and the thickness of the quantum well GaAs equal to 55 , provides the sensitivity of the photodetector in the range of 8-12 microns.

The photodetector operates as follows.

In the state of thermodynamic equilibrium electrons with energy levels in the silicon layer in the layer i-AlxGa1-xAs moving to a lower level n layer, an i-GaAs. When the direction of the external radiation with energy h, sufficient to excite the proportion n of these electrons in the free state (continuous continuum of energies), the superlattice creates a conductive state. With application of an external voltage between the first and second contact layers in the sensor occurs, the system is .

When this parasitic factor is only the recombination of free electrons in the energy levels of the in-layer and quantum well n. The dark current is weakened, on the one hand, the effect explode quantum wells due to the increase of the barrier, on the other hand, due to the exclusion of hopping conductivity by impurity States between quantum wells.

Emergency a few times recombination at the level calls for the constant population of n levels, which ultimately leads to the increase of the quantum yield. The use of the invention will improve detecting ability and the ratio signal/noise photodetectors.

PHOTODETECTOR-BASED SEMICONDUCTOR STRUCTURES WITH QUANTUM WELLS, comprising a substrate of semi-insulating GaAs buffer layer, an i - GaAs first contact layer of n - GaAs, a system of alternating layers of AlxGa1-xAs and GaAs, and in one of the materials system of alternating layers of introduced impurity silicon to the doping level of 2 1018cm-3and the second contact layer of n - GaAs, characterized in that the silicon is introduced into the layer of AlxGa1-xAs in the form of a monatomic layer, located at a distance not larger Debye length Ukranian

 

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