RU2671286C1 - Semiconductor structure for photo-conducting antennas - Google Patents

Abstract

FIELD: antenna equipment.

SUBSTANCE: invention can be used in the production of transmitting and receiving antennas for the terahertz frequency range (from 300 GHz to 5 THz). Semiconductor structure for photoconducting antennas is epitaxially grown on a GaAs substrate with crystallographic orientation (111)A and consists of alternating layers of undoped low-temperature LT-GaAs and high-temperature silicon-doped GaAs:Si hole-type conductivity. LT-GaAs layers are grown at a ratio of arsenic and gallium fluxes greater than GaAs:Si layers doped with silicon and grown in a high-temperature regime.

EFFECT: invention makes it possible to control the concentration of point defects As_Ga and thus the possibility of controlling the lifetime of photoexcited charge carriers by growing matrix matrix layers of LT-GaAs at elevated arsenic pressure.

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Description

FIELD OF THE INVENTION

The invention relates to semiconductor structures based on compounds of group A ³ B ⁵ with photoconductivity properties and with an extremely short lifetime of photoexcited charge carriers (less than 0.5 ps). Such semiconductor structures can be used in the manufacture of transmitting and receiving antennas for the terahertz frequency range (from 300 GHz to 5 THz).

BACKGROUND

The following types of structures can be used as structures for photoconductive antennas:

1. Semi-insulating (PI) GaAs (100) substrates subjected to implantation of arsenic ions (As) or gallium (Ga), oxygen (O), silicon (Si), carbon (C) at ion implantation installations [Hark No Tan, Chennupati Jagadish , Krzyszton Priotr Korona, Jacek Jasinski, Maria Kaminska, Rimas Viselga, Saulius Marcinkevicius, Arunas Krotkus. Ion-implanted GaAs for subpikosecond optoelectronic applications // IEEE Journal of selected Topics in Quantum Electronics. - 1996. - V. 2. - N. 3. - P. 636-642] [Tze-An Liu, Masahico Tani, Ci-Ling Pan. THz radiation emission properties of multienergy arsenic-ion-implanted GaAs based photoconductive antennas // J. Appl. Phys. - 2003. - V. 93. - N. 5. - P. 2996-3001] [Arunas Krotkus. Semiconductors for terahertz photonics applications. J. Appl. Phys. D: Appl. Phys. - 2010. - V. 43. - P. 273001] [Prathmesh Deshmukh, M. Mendez-Aller, Abhishek Singh, Sanjoy Pal, S.S. Prabhu, Vandana Nanal, R.G. Pillay, G.H. Dohler, S. Preu. Continuous Wave terahertz radiation from antennas fabricated on C12-irradiated semi-insulating GaAs // Optics Letters. - 2015. - V. 40. - N. 19. - P. 4540-4543]. The disadvantages of this structure is that ion implantation produces a large number of defects that reduce the dark resistivity of the structure and the mobility of charge carriers.

2. Another type of material showing subpicosecond carrier capture time is a structure containing self-organizing ErAs islands in a GaAs matrix. When GaAs are doped with erbium atoms with a concentration higher than their solubility limit in GaAs, excess Er forms nanosized ErAs precipitates (like the well-known InAs quantum dots in a GaAs matrix). In the works of [S. Kadow, S.B. Fleischer, J.P. Ibbetson, J.E. Bowers, A.C. Gossard, J.W. Dong, C.J. Palmstrom. Self-assembled ErAs islands in GaAs: growth and subpicosecond carrier dynamics. Appl. Phys. Lett. - 1999. - V. 75. - N. 22. - P. 3548-3550] [C. Kadow, A.W. Jackson, A.C. Gossard, S. Matsuura, G.A. Blake Self-assembled ErAs islands in GaAs for optical-heterodyne THz generation // Appl. Phys. Lett. - 2000. - V. 76. - N. 24. - P. 3510-3512] [Christoph Kadow, Andrew W. Jackson, Arthur C. Gossard, John E. Bowers, Shuji Matsuura, Geoffrey A. Blake. Self-assembled ErAs islands in GaAs for THz applications // Physica E. - 2001. - V. 7. - P. 97-100] presents the technology for creating a structure that is essentially a GaAs / ErAs superlattice: that is, in a GaAs matrix ErAs islands from 0.6 to 1.2 ML thick (monolayers) are created, separated by GaAs layers 20, 40, or 60 nm thick. The periods of such superlattices were also 20, 40, and 60 nm. We studied superlattice structures with the following parameters and periods of such superlattices: 20 × (1.2 ML ErAs / 40 nm GaAs), 40 × (1.2 ML ErAs / 40 nm GaAs), 60 × (1.2 ML ErAs / 20 nm GaAs).

The disadvantage of such structures is the need for the molecular beam epitaxy (MBE) installation to have a molecular source Er, which for a number of reasons has not been widely used in MBE technology. In addition, structural quality problems arise in the case of ErAs island thicknesses of the order of or more than 3 ML [C. Kadow, S.B. Fleischer, J.P. Ibbetson, J.E. Bowers, A.C. Gossard, J.W. Dong, C.J. Palmstrom. Self-assembled ErAs islands in GaAs: growth and subpicosecond carrier dynamics // Appl. Phys. Lett. - 1999. - V. 75. - N. 22. - P. 3548-3550]. In this case, the structural quality of the structure deteriorates with each overlying GaAs layer grown over ErAs islands.

3. The most common structure is a GaAs film epitaxially grown at a low temperature of 150-350 ° C (low-temperature GaAs, LT-GaAs), while the standard temperature of epitaxial growth of GaAs is 450-600 ° C. To grow such structures, GaAs or Si substrates with a crystallographic orientation of (100) are used [Patent US 7364993 B2. Method of enhancing the photoconductive properties of a semiconductor / Michael J. Evans, William R. Tribe; TeraVieW Limited, Cambridge. - Appl. No. 10/527313; filling date 09/11/2003; publication date 04/29/2008].

The main feature of structures based on LT-GaAs and structures based on ion-implanted arsenic (As) GaAs substrates is the presence in the crystal structure of excess arsenic atoms, which can reach up to 2 atomic%.

It is known that an excess of arsenic atoms (As) in the crystalline structure of LT-GaAs and GaAs substrates ion-implanted with As ions leads to the formation of the following intrinsic defects in GaAs-based structures: an arsenic atom at the site of a gallium atom (As _Ga ), an interstitial atom of arsenic ( As _i ); gallium atom vacancy (V _Ga ). But the main defect responsible for the capture of photoexcited electrons and a decrease in their lifetime is the As _Ga defect [A. Krotkus, K. Bertulis, L. Dapkus, U. Olin, S. Marcinkevicius. Ultrafast carrier trapping in be-doped low-temperature-grown GaAs // Appl. Phys. Lett. - 1999. - V. 75. - P. 3336-3338]. But in order to capture an electron, an As _Ga defect must be in a charged state of As _Ga ⁺ or As _Ga ⁺⁺ .

In order to increase the concentration of charged defects, an LT-GaAs-based structure is doped with beryllium. Beryllium atoms in GaAs are acceptors. This means that they form unfilled energy levels in the band gap near the ceiling of the valence band, to which electrons from As _Ga defects pass, due to which As _Ga defects pass into the charged state As _Ga ⁺ or As _Ga ⁺⁺ [Patent US 8835853. Photoconductive element / Toshihiko Ouchi, Kousuke Kajiki; Canon Kabushiki Kaisha, Tokyo. - Appl. No. 13/416447; filling date 03/09/2012; publication date 09.16.2014]. [CH Goo, WS Lau, TC Chong, LS Tan. Trap signatures of As precipitates and As-antisite-related defects in GaAs epilayers grown by molecular beam epitaxy at low temperatures. Appl. Phys. Lett. - 1996. - V. 69. - N. 17. - P. 2543-2545] [P. Specht, S. Jeong, H. Sohn, M. Luysberg, A. Prasad, J. Gebauer, R. Krause-Rehberg, ER Weber. Defect control in As-rich GaAs // Material Science Forum. - 1997. - V. 258-263. - P. 951-956] [J.-L. Coutaz, JF Roux, A. Gaarder, S. Marcinkevicius, J. Jasinski, K. Korona, M. Kaminska, K. Bertulis, A. Krotkus. Be-doped low-temperature grown GaAs for ultrafast optoelectronic devices and applications. XI International Semiconducting and Insulating Materials Conference 3-7 July 2000. The Australian National University, Canberra, Australia. P. 89-96].

However, beryllium, used in compounds A ³ B ⁵ as an acceptor type dopant, is a hazard class 1 substance [Maximum permissible concentrations of harmful substances in the air of the working area: hygienic standards GN 2.2.5.1313-03: approved. The chief state sanitary doctor of the Russian Federation 04/27/2003: introduction. effective April 30, 2003. - M., 2003]. Therefore, the use of beryllium in molecular beam epitaxy units requires the observance of additional safety measures. In addition, the presence of a beryllium source in the molecular beam epitaxy unit leads to an increase in the background p-type impurity in all structures that are subsequently grown in such a unit. This circumstance causes further difficulties in growing structures with an extremely low content of unintentional impurities. This is especially true when high breakdown voltage is required on structures.

The closest in technical essence and also adopted for the prototype is the structure described in [Patent for the invention No. 2624612. Semiconductor structure for photoconductive antennas / Galiev Galib Barievich, Klimov Evgeny Aleksandrovich, Maltsev Petr Pavlovich, Pushkarev Sergey Sergeevich. - priority of the invention 07.10.2016; date of state registration in the State Register of Inventions of the Russian Federation 07/04/2017]. The structure is a semiconductor epitaxial multilayer structure grown on a GaAs substrate with a crystallographic orientation of (N11) A, where N = 1, 2, 3 ..., consisting of alternating matrix layers of undoped GaAs grown in a low temperature mode and functional GaAs layers grown in standard high temperature and doped with Si atoms. Initially, the ratio of arsenic (As) and gallium (Ga) fluxes γ (γ = P _As / P _Ga , where P _As and P _Ga are the partial pressure of the molecular flows of arsenic and gallium, respectively) is chosen so that GaAs layers exhibit high-temperature epitaxial growth p-type conductivity. The concentration of charge carriers (in our case, holes) is controlled by a change in the thickness of silicon-doped GaAs layers grown in the standard high-temperature regime, as well as by a change in the repetition period of these layers. The disadvantage of this structure is the inability to control the concentration of excess arsenic, and hence the concentration of As _Ga anti-structural defects in LT-GaAs, which are the most important parameter of LT-GaAs-based structures, which essentially determines the characteristics of GaAs-based photoconductive materials. Since the structure in this case is grown at a fixed value of γ, which is limited from above by obtaining p-type conductivity in high-temperature layers.

SUMMARY OF THE INVENTION

The objective of the invention is to obtain a structure for photoconductive antennas, which could significantly expand the capabilities of the structure grown on a GaAs substrate with a crystallographic orientation of (111) A, consisting of alternating matrix layers of undoped GaAs grown in low temperature mode and functional GaAs layers grown in standard high temperature and doped with Si atoms. The ratio of arsenic and gallium fluxes during epitaxial growth in this case is chosen so that in the high-temperature regime of epitaxial growth, GaAs layers exhibit p-type conductivity. That is, the structure is essentially a {LT-GaAs / GaAs: Si} superlattice. An important point in such a structure is that it is grown at a fixed ratio of arsenic and gallium fluxes, that is, at a constant value of γ.

The concentration of charge carriers (in this case, holes) is controlled by a change in the thickness of silicon-doped GaAs layers grown in the standard high-temperature regime, as well as by a change in the repetition period of these layers. For this, the proposed structure must have a lifetime of photoexcited charge carriers and a specific dark resistance comparable with similar parameters of the structure based on the {LT-GaAs / GaAs: Si} superlattice. The technical result is the technological ability to control the concentration of point defects As _Ga .

The technical result is achieved due to the fact that periodically arranged GaAs functional layers epitaxially grown in the high temperature mode and doped with Si atoms are embedded in an LT-GaAs film epitaxially grown in a low-temperature mode on a GaAs substrate with a (111) A crystallographic orientation. In this case, the initial ratio of arsenic and gallium fluxes (γ ₁ ) during epitaxial growth is chosen such that, in the high-temperature epitaxial growth mode, silicon-doped GaAs: Si layers exhibit p-type conductivity in the case of growth on a (111) A crystallographic surface. The growth of other periods of the superlattice, namely, the low-temperature layers of LT-GaAs, is carried out at elevated arsenic pressure (i.e., when γ _LT-GaAs > γ _{GaAs: Si} ). This will lead to the fact that the amount of excess arsenic, and ultimately, the concentration of As _Ga point defects in LT-GaAs layers can be technologically controlled by changing (increasing) the arsenic pressure during the growth of these structure layers.

The concentration of acceptor impurities in our structure can be controlled in the following ways: 1) by controlling the thicknesses of high-temperature silicon-doped layers of the GaAs structure: Si or the superlattice period {LT-GaAs / GaAs: Si}; 2) by raising or lowering the temperature of the Si source in the MBE installation; 3) by increasing or decreasing the growth temperature of the functional layers. The indicated methods for controlling the concentration of holes in the proposed structure will lead to the possibility of controlling the concentration of ionized defects As _Ga ⁺ and As _Ga ⁺⁺ , and thereby to the possibility of controlling the lifetime of photoexcited charge carriers.

The regulation of the lifetime of photoexcited charge carriers in the proposed structure is also possible by changing the ratio of arsenic and gallium fluxes γ. With increasing arsenic pressure P _As (and, therefore, increasing γ) during the growth of LT-GaAs layers, the amount of excess arsenic in them increases, and consequently, the concentration of As _Ga defects, and hence the concentration of charged defects As _Ga ⁺ or As _Ga ⁺⁺ . Thus, the proposed structure allows one to grow a structure with a technologically controlled concentration of charged As _Ga defects.

BRIEF DESCRIPTION OF THE DRAWING

In FIG. 1 is a cross-sectional diagram of a semiconductor structure selected for the prototype: a GaAs 1 substrate with a crystallographic orientation of the (111) A surface, LT-GaAs 2 matrix layers and p-GaAs: Si 3 functional layers are indicated.

DETAILED DESCRIPTION OF THE INVENTION

The invention consists in the fact that by the method of molecular beam epitaxy on a GaAs substrate with a crystallographic orientation of the surface (111) A, a structure (Fig. 1) is grown with a total thickness of 1 to 3 μm, consisting of LT-GaAs matrix layers with a thickness of 165 to 280 nm grown at temperatures from 140 to 300 ° C with a ratio of arsenic and gallium fluxes P _As / P _{G a} = γ ₁ (γ ₁ > 30), between which are located equidistant functional GaAs: Si layers from 50 to 100 nm thick, grown at temperature from 450 to 520 ° C and uniformly doped with Si atoms. When growing GaAs: Si layers, the ratio of arsenic and gallium fluxes γ ₂ (10 <γ ₂ <25) is chosen such that the functional high-temperature GaAs: Si layers have a hole type of conductivity.

As a specific implementation of the invention, a structure with a total thickness of 1 μm consisting of 230 nm thick LT-GaAs matrix layers grown at a temperature of 200 ° C and arsenic flux ratio was grown on a GaAs substrate with a crystallographic orientation of (111) A by molecular beam epitaxy on a GaAs substrate and gallium γ from 20 to 60. Between the matrix layers are equidistant GaAs functional layers with a thickness of 20 nm, grown at a temperature of 480 ° C and uniformly doped with Si atoms. Before epitaxial growth of each subsequent layer of the structure, growth was stopped, the growth temperature changed (that is, the temperature to which the structure was heated), the ratio of arsenic and gallium fluxes corresponded to the LT-GaAs (γ ₁ ) or GaAs: Si (γ ₂ ) layers. Γ ₂ = 10 was chosen in which the functional high-temperature GaAs layers uniformly doped with silicon atoms have hole (p-) type of conductivity.

Measurements of electrophysical parameters showed that the grown structure has a hole (p-) type of conductivity with a hole concentration of N _p = 1.16⋅10 ¹⁶ cm ^-3 and hole mobility μ _p = 80 cm ² / (V⋅c). Thus, due to the introduction of functional layers, a change in the technological growth conditions (growth temperature, and the ratio of arsenic and gallium fluxes) of LT-GaAs and GaAs: Si layers and the use of GaAs substrates with (111) A orientation, favorable conditions are created for the ionization of point defects As _Ga , formed in the matrix layers, and therefore, for the active capture of photoexcited electrons by ionized point defects. In addition, and this is the most important thing, the proposed structure implements the possibility of technological control of the concentration of As _Ga point defects by growing LT-GaAs matrix layers under increased arsenic pressure.

Claims (1)

A semiconductor structure for photoconductive antennas grown epitaxially on a GaAs substrate with a (111) A crystallographic orientation and consisting of alternating layers of undoped low-temperature LT-GaAs and high-temperature silicon-doped GaAs: Si hole type conductivity, characterized in that the LT-GaAs layers are grown at a ratio arsenic and gallium fluxes are larger than GaAs: Si layers doped with silicon and grown in a high-temperature regime.

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