RU2065224C1 - Semiconductor heteroepitaxial structure for photodetecting cell - Google Patents

Abstract

FIELD: semiconductors, in particular, construction of heteroepitaxial structure. SUBSTANCE: semiconductor heteroepitaxial structure for photodetecting cell uses a monocrystalline substrate with a heteroepitaxial layer of n-type semiconductor located on it, the layer on the boundary of separation being disrupted. This layer has two layers of highly doped n+-type semiconductor, the thickness of the first layer being equal to that of the disrupted layer. The first layer is located on the boundary of separation with the substrate, and the second layer is a tunnel - opaque one for minority carriers and positioned at a distance equal to the doubled length of Debye shielding from the first one. A p+ layer is formed in the gap between the first and second n+ layers. EFFECT: improved structure. 2 dwg

Description

 The invention relates to semiconductor devices, in particular to the design of a photodetector cell based on a MIS structure.

Known semiconductor heteroepitaxial structures for photodetector cells with InGaAs or InAsSb layers on wide-gap substrates [1]
A disadvantage of the known structures is the low detection ability due to the high rate of generation of charge carriers at the interface with the substrate.

Closest to the proposed one is a semiconductor heteroepitaxial structure for a photodetector cell, including an n-type gallium arsenide substrate, an n-type indium antimonide layer placed on it [2]
A disadvantage of the known semiconductor heteroepitaxial structure is the intensive generation of minority carriers in the disturbed layer at the interface with the substrate, which results in a low detection ability of the photodetector cell.

EFFECT: increased detection ability — is achieved by the fact that the known semiconductor heteroepitaxial structure for a photodetector cell, including an n-type gallium arsenide substrate, an n-type InSb heteroepitaxial layer placed on it, contains an additionally doped n ⁺ -type layer located at the interface with substrate and having a thickness equal to the thickness of the broken layer, a heavily doped p ⁺ type layer with a thickness equal to twice the length of the Debye screening, located above the first h ⁺ layer, W A second n ⁺ layer is tunnel opaque to minority carriers located above the p ⁺ layer.

The heteroepitaxial layers of compounds A ₃ B ₅ , A ₄ B ₆ , A ₂ B ₆ can be used as the active layer, and semiconductor and dielectric materials, heteroepitaxial structures with buffer dielectric layers as substrates.

 In FIG. 1 and 2 show the cross section of the heteroepitaxial structure and its band diagram.

On the monocrystalline substrate 1 (Fig. 1), an h ⁺ layer 2 of semiconductor thickness d ₁ , a layer 3 of a p ⁺ type thickness D ₂ , a layer 4 of a h ⁺ type thickness D ₃ , an active layer 5 of a semiconductor are successively arranged. In FIG. Figure 2 shows the band diagram of a heteroepitaxial structure with heavily doped layers. Designated: E _c , E _v , E _f , E _{g the} bottom of the conduction band, the valence band ceiling, the Fermi level and the band gap, respectively. Ф value of potential barrier for holes.

The heteroepitaxial structure works as follows: when illuminating the active region 5 of the heterostructure, electron-hole pairs are formed in it. As cells of the FPU in the active layer of a semiconductor, MIS or diode structures are usually used, operating on the basis of separation of the main and minor charge carriers with the accumulation or registration of the latter. Holes arising due to dark generation in the defective region near the interface will not be able to get into the active region 5 due to the presence of a potential well formed by the p ⁺ region and will not affect the operation of the FPU cell formed in the active layer.

10¹² см^-2 для гетеросистемы InSl/GaSs, быстро уменьшается с ростом толщины до

, а затем плавно спадает по гиперболическому закону. При этом время жизни (время генерации) неосновных носителей обратно пропорционально плотности дислокаций τ_d= Nd^-1 [с.]; при достаточном удалении от границы раздела Nd уменьшается настолько, что τ_d становится равным времени слиточного бездислокационного материала. Это происходит при толщинах d₁ 3-5 мкм.The thickness of the first n ⁺ layer of the semiconductor is chosen equal to the thickness of the broken layer, which is determined by the region with a high dislocation density Nd. The value of Nd at the interface reaches the values of Nd

10 ¹² cm ^-2 for the InSl / GaSs heterosystem, decreases rapidly with increasing thickness to

, and then gradually decreases according to the hyperbolic law. In this case, the lifetime (generation time) of minority carriers is inversely proportional to the dislocation density τ _d = Nd ^-1 [s]; at a sufficient distance from the interface, Nd decreases so much that τ _d becomes equal to the time of the ingot dislocation-free material. This occurs at thicknesses d ₁ 3-5 microns.

The thickness of the second n ⁺ layer is selected from the condition that there is no tunneling of holes through this region. In this region, intense recombination of holes trapped in the n ⁺ p ⁺ junction occurs.

The thickness of the p ⁺ layer is chosen equal to twice the length of the Debye screening. The optimal values of d ₃ and d ₂ can be chosen the same and equal to d ₃ d ₂ 0.2 μm, and the thickness of the first h ⁺ layer is chosen such that the generation due to dislocations at a distance d ^ from the interface corresponds to the density of the generation current in a bulk material.

 The proposed design has the following advantages compared to the prototype.

1. The presence of the first heavily doped n ⁺ layer leads to a decrease in the generation current in this region due to a decrease in the generation-recombination process. In addition, this n ⁺ layer with a thickness of 5 μm makes it possible to get rid of intrinsic light absorption in this region due to the Moss-Burstein shift when the active region is illuminated through a wide-gap substrate and provides ohmic contact on semi-insulating GaAs substrates or other dielectric substrates.

(1)
Проведем численные оценки для узкозонного п/п InSb, для которого при Т 77 К ΔΦ = 0,2 эВ, и собственная концентрация дырок в бездефектном п/п

см^-3.2. The presence of the p ⁺ region leads to the formation of a potential barrier for holes and a potential barrier formed by the p ⁺ region and the second n ⁺ region of Φ = E ₉ + ΔΦ, where E _g is the semiconductor band gap, and ΔΦ is the potential barrier, determined by the Moss-Burstein shift. For most semiconductors in a reasonable doping range, Dv = 0.1-0.2 eV. The hole concentration in region 5 is determined by p ⁺ and the potential barrier Φ

(one)
We carry out numerical estimates for the narrow-gap InSb subband, for which at T 77 K ΔΦ = 0.2 eV, and the intrinsic concentration of holes in a defect-free semiconductor

cm ^-3 .

(3)
τ_d "дислокационное" время жизни (генерации), τ_o время жизни бездислокационного материала, L_p диффузионная длина дырок, d - расстояние от границы раздела с подложкой до активного слоя. Видно, что концентрация дырок в активном слое существенно превышает собственную концентрацию P_i при любой температуре.a) In the absence of additional heavily doped layers, the concentration of holes in the active layer can be estimated by the formula
P ₅ (act.) P _gr • exp (-d / L _p ≈ 10 ¹⁵ cm ^-13 , (2)
where P _{gr the} concentration of holes at the interface, equal to

(3)
τ _{d is the} “dislocation” lifetime (generation), τ _{o is} the lifetime of a dislocation-free material, L _{p is the} diffusion length of holes, d is the distance from the interface with the substrate to the active layer. It can be seen that the hole concentration in the active layer substantially exceeds the intrinsic concentration P _i at any temperature.

т. е. дырки из дефектной и p⁺-областей практически не будут попадать в активный слой 5, где их концентрация может считаться равной собственной, т. е. приблизительно 10¹⁰ см^-3.b) In the presence of an n ⁺ -p ⁺ junction, the hole concentration in the active region 5 will be equal to

that is, holes from the defective and p ⁺ regions will practically not fall into the active layer 5, where their concentration can be considered equal to the intrinsic layer, i.e., approximately 10 ¹⁰ cm ^-3 .

а концентрация дырок, заброшенных через n⁺-p⁺-барьер величиной Φ, равной F = E₉+ ΔΦ как

то видно, что собственная концентрация дырок растет быстрее, чем концентрация дырок, попадающих из дефектной области (из p⁺-области).An increase in the working temperature from 77 to 200 K leads to a simultaneous increase in both the intrinsic concentration of holes in region 5 and their casting into the active region from the p ⁺ region. However, since the intrinsic concentration p _i increases with temperature as

and the concentration of holes abandoned through an n ⁺ -p ⁺ barrier with a value Φ equal to F = E ₉ + ΔΦ as

it can be seen that the intrinsic concentration of holes grows faster than the concentration of holes falling from the defective region (from the p ^{+ region} ).

3. The presence of the second n ^{+ region} leads to an additional increase in the recombination process of holes falling from the p ^{+ region} ; the presence of a sharp n ⁺ p ⁺ n ⁺ junction in narrow-gap semiconductors with a small effective mass leads to low-ohmic characteristics of this junction due to tunneling current passage; leads to a more efficient collection of holes in the active region 5 due to the presence of a potential barrier ΔΦ preventing the exit of “light” holes from region 5 to the substrate.

Thus, the use of the n ⁺ p ⁺ n ⁺ structure leads to a significant decrease in the generation current due to structural defects arising from heteroepitaxy to the active region. A weak temperature dependence makes it possible to significantly increase the operating temperatures of the FPU, since in this design the intrinsic concentration determined by the fundamental parameters of the semiconductor grows faster than the hole throwing through the potential barrier.

 4. Since the equations describing the generation, diffusion, and recombination processes are the same for all types of semiconductors, and misfit dislocations occur in all heterosystems without exception, this design will work in all semiconductor layers on any substrates.

As the material for the active layer, not only InSb or InAs, but also any other photosensitive semiconductor material can be used, for example, InGaAs, InGaSb, InAsSb, compounds A ₂ B ₄ , A ₄ B ₆ and others that can be obtained by heteroepitaxial single crystal substrates. The substrates can be dielectric and semiconductor materials on which heteroepitaxial growth is possible: for example, GaAs, Si, Ge, etc.

The most promising is the use of silicon substrates with buffer layers of barium, strontium or calcium fluorides grown on them. In all cases, the density of misfit dislocations at the film – substrate interface is determined by the mismatch of the constant film – substrate lattices. Accordingly, the thickness of the defective layer will vary in various heterosystems. However, choosing the thickness of the first heavily doped n ⁺ layer equal to the thickness of this defective (dislocation) layer for a particular heterosystem and leaving the other criteria of the p ⁺ and second n ⁺ layer unchanged, the same positive result is achieved.

 Thus, with an increase in the lifetime (decrease in the generation current) in the active region, the detecting ability of the photodetector cell increases.

Claims (1)

A semiconductor heteroepitaxial structure for a photodetector cell, comprising a single crystal substrate, an heteroepitaxial layer of an n-type photosensitive semiconductor with a broken layer at the interface, characterized in that the heteroepitaxial layer additionally contains two heavily doped n ⁺ layers, the first thickness equal to the thickness of the broken layer , is located at the interface with the substrate, the second is made tunnel-opaque for minority hole carriers and placed at a distance of lshem double Debye screening length of the first and between the first and second n ^+-shells is p ⁺ -layer.

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