RU2531551C2 - Multi-epitaxial structure of double-injection high-voltage hyper-fast recovery diode chip based on gallium and arsenic - Google Patents

Abstract

FIELD: physics.

SUBSTANCE: invention relates to semiconductor devices. A multi-epitaxial structure of a double-injection high-voltage hyper-fast recovery diode chip based on gallium and arsenic compounds comprises a heavily doped monocrystalline substrate of p⁺-type conductivity, with differential concentration of acceptor and donor dopants of not more than 3·10¹⁸ cm^-3 and thickness of not more than 200 mcm, an epitaxial GaAs layer made thereon, having p-type conductivity with thickness of not more than 5.0 mcm and differential concentration of donor and acceptor dopants which varies from concentration in the substrate to values of not more than $$\sqrt{\mathrm{2,22}}\cdot {10}^{11}c{m}^{-3},$$

an epitaxial GaAs i-layer with thickness of 5-100 mcm having p-n-junction type conductivity and a space-charge region, and an inner-lying multi-epitaxial metal junction area, and an epitaxial GaAs layer on a p-n junction epitaxial i-layer, having n⁺-type conductivity with differential concentration of acceptor and donor dopants in the surface layer of not less than 1·10¹⁷ cm^-3 and thickness of not less than 0.1 mcm.

EFFECT: invention prevents forward potential drop, increases forward biasing current and operating speed.

2 cl, 3 dwg

Description

The invention relates to the field of semiconductor devices, in particular, to the design of high-current ultrafast recovery diodes (UFRED) and hyperfast recovery diodes (Hyper-FRED) high-voltage diodes with low forward voltage drops, high operating temperature, low recovery times for reverse switching current. In high-frequency power factor correctors for high-frequency secondary power sources, in a frequency-controlled electric drive, in RF rectifiers and other devices, fast-recovery gallium arsenide (GaAs) diodes are used with a design similar to Schottky diodes or bipolar diodes made on epitaxial bipolar or GaAs material diffusion-drift mechanism of charge carrier transfer. Schottky diodes based on gallium arsenide (GaAs) are manufactured by IXYS (USA) (www.ixys.com) and TT Electronics Semelab (www.semelab.com). These diodes have significant limitations on the maximum allowable currents (≤50 A / chip), voltages (up to 250 ÷ 300 V) due to structural imperfections of GaAs epitaxial structures used by MOCVD and, as a consequence, the low reliability of the Schottky-semiconductor transition; Another serious limitation is the rather high Schottky-junction barrier capacitance, which limits the switching frequency ceiling of these diodes and, therefore, the applicability in high-frequency converters.

The closest technical solution is the crystal structure of a power diode based on gallium arsenide compounds described in United States Patent No. 5,733,815, Mar. 31, 1998, authors G.A. Ashkinazi et al. [1]. The crystal of the power diode shown in the above copyright certificate (anode part) contains a single-crystal substrate of p ⁺ gallium arsenide of conductivity uniformly doped with zinc with a concentration of more than 5 × 10 ¹⁸ cm ^-3 . The p-type and n-type layers of gallium arsenide are deposited onto the specified single-crystal substrate by liquid epitaxy, while the p-type conductivity of the epitaxial layer has a thickness of at least 10 μm, and the n-type epitaxial layer (cathode part) has a thickness of at least 15 μm . Between the epitaxial layers of p- and n-types of conductivity there is a region with a difference concentration of acceptor and donor impurities of less than 10 ¹² cm ^-3 , the difference concentration of acceptor and donor impurities in the p-type epitaxial layer, in this case zinc, gradually decreases from the value 5 · 10 ¹⁸ cm ^-3 , at the interface, the single crystal substrate is the epitaxial layer to a difference concentration of acceptor and donor impurities of less than 10 ¹² cm ^-3 . Next, there is an epitaxial i-region 3–70 μm thick with a difference concentration of donor and acceptor impurities of less than 10 ¹² cm ^-3 , and an epitaxial layer (cathode part) of n-type with a thickness of at least 15 microns is created in this single process with a smooth increase in the differential concentration from 10 ¹² cm ^-3 to values of 1.0 · 10 ¹⁶ cm ^-3 . The limitation of the difference concentration of the donor and acceptor impurities to 10 ¹⁶ cm ^–3 is due, according to the authors of [1], to a sharp increase in the dislocation density of the epitaxial GaAs crystal lattice, which leads to a significant decrease in the reverse voltage.

Inside the i-region is a metallurgical pn junction with a difference concentration of donor and acceptor impurities of less than 10 ¹² cm ^-3 . The width of this region is in the specific case [1] at maximum reverse voltages 200 ÷ 700 V - 3 ÷ 15 μm, 700 ÷ 1500 V - 30 ÷ 50 μm, 1500 ÷ 2000 V - 40 ÷ 60 μm.

The specified technical solution [1] has a number of conflicting requirements and disadvantages:

one). "... the maximum value of the difference concentration in the n-type epitaxial layer that occurs on the surface of the diode should not exceed 10 ¹⁶ cm ^-3 , otherwise, due to an increase in the density of dislocations, the reverse voltage decreases." [one]

But it is known that at a surface concentration of n-type GaAs epitaxial or single-crystal substrates less than 10 ¹⁸ cm ^-3 it is extremely difficult to create a good ohmic contact or non-rectifying contact with a low parasitic resistance, but this is impossible, but this contradicts the formula and design of the known solution [ 1], aimed at increasing the maximum currents per unit area of the GaAs diode.

2). The presence of a smoothly decreasing concentration of the acceptor impurity in the solution [1], in this case zinc, in the p-type epitaxial layer from values of 5 · 10 ¹⁹ cm ^-3 to 10 ¹² cm ^-3 from the interface to the region with a difference concentration of 10 ¹² cm ^{- 3 is} not a guarantee of a sharp decrease in the density of dislocations in a p-type conductivity layer, which affects the level of dislocations in the region between p and n epitaxial layers with a difference concentration of 10 ¹² cm ^-3 , and this affects the maximum allowable reverse stresses. The higher the content of acceptor impurity (Zn) in the p ⁺ substrate, the higher the level of imperfection of the substrate.

3). The limiting volumetric difference concentration of donor and acceptor impurities in the n-type epitaxial layer specified in the known solution [1] is 1.5 · 10 ¹⁵ cm ^-3 ÷ 1.0 · 10 ¹⁶ cm ^-3 and, therefore, the required thickness of the high-resistance epitaxial layer n-type conductivity, due to the significant width of the space-charge region, leads to a sharp decrease in the possibility of creating highly efficient high-speed, with hyper-small recovery times for reverse current GaAs diodes (<50 nanoseconds), in particular, in the operating voltage range 600 ÷ 800 for creating ultra-phase diode bridge and giperbystryh and half-bridges for high-frequency converters with a switching frequency to 2.0 MHz, and the single-phase inverters that are based on the combined high-keys in GaAs diodes.

four). The presence of a thick high-resistance and epitaxial n-type layer in the known solution [1] is an extremely important factor limiting the performance of this p-i-n GaAs structure and reducing the efficiency of carrier injection of p-i-n GaAs structures.

The technical result of this invention is:

- reduction of direct voltage drop of the current-voltage characteristics;

- a sharp increase in direct current current density;

- increased performance to the level of several tens of nanoseconds.

The technical result is achieved by the fact that in the known solution [1] a high n-type epitaxial layer adjacent to the i-region is eliminated, and epitaxial highly doped n ⁺ -type conductivity layers from GaAs compounds or GaAs and AlGaAs combinations (aluminum compounds, gallium and arsenic) doped with such impurity atoms forming donor levels as silicon (Si), tellurium (Te), tin (Sn), with a doping level several orders of magnitude higher than in the i-region adjacent to them.

The solution to this problem lies in the fact that, in contrast to the well-known solution of the GaAs power diode [1], which contains a highly doped single-crystal GaAs substrate of 1 p ⁺ conductivity type with a difference concentration of acceptor and donor dopants of ≥5 · 10 ¹⁸ cm ^-3 , which has been successively performed: epitaxial GaAs p-type layer of conductivity 2 with a varying differential concentration of acceptor and donor dopants from 5 · 10 ¹⁸ cm ^-3 to a differential concentration of not more than 10 ¹² cm ^-3 and a thickness of not less than 10 microns; pn — transition epitaxial GaAs i-layer 3 with a thickness of 3–70 μm with a space charge region and an internal multi-epitaxial metallurgical pn junction with a difference concentration of acceptor and donor dopants of not more than 10 ¹² cm ^–3 ; a high-resistance epitaxial GaAs layer of n-type conductivity 4 with a varying difference concentration of acceptor and donor dopants from the level at the interface with the pn transition i-layer to a level of 10 ¹⁶ cm ^-3 and a thickness of at least 15 μm, the following is fulfilled:

- a highly doped single-crystal GaAs substrate of 1 p ⁺ conductivity type has a differential concentration of acceptor and donor dopants of at least 3 × 10 ¹⁸ cm ^-3 and a thickness of at least 200 μm;

(*3начение корня квадратного от количества атомов в 1,0 см³ арсенида галлия);- the p-type conductivity epitaxial layer 2 has a thickness of at least 5.0 μm and contains a varying differential concentration of acceptor and donor dopants from the concentration of dopants in the single-crystal p ⁺ type conductivity of the GaAs substrate to values no more than

(* 3 the value of the square root of the number of atoms in 1.0 cm ³ gallium arsenide);

;- pn conductive transition epitaxial GaAs i-layer 3, having a thickness of 5.0 ÷ 100 μm, containing a space charge region and an intra-located multi-epitaxial metallurgical transition zone with a difference concentration of acceptor and donor dopants in the multi-epitaxial metallurgical transition zone less than or equal to

;

- the high-resistance epitaxial GaAs layer 4 of n-type conductivity made on the i-epitaxial layer 3 with a varying difference concentration of acceptor and donor dopants from the concentration of impurities at the interface with the i-transition layer 3 is excluded from the design of the known solution [1] pin GaAs diode up to 10 ¹⁶ cm ^-3 and a thickness of at least 10 microns;

- instead of the high-resistance epitaxial GaAs layer 4 of the n-type conductivity, one of the two following structural and technological solutions is introduced:

1) a highly doped epitaxial GaAs layer of 5 n ⁺ -type conductivity with a differential concentration of acceptor and donor dopants in the surface layer of at least 10 ¹⁷ cm ^-3 and a thickness of at least 0.1 μm;

2) or - two consecutive high-doped n ⁺ -type conductivity of the epitaxial layer: GaAs buffer epitaxial layer 5 with a differential concentration of acceptor and donor dopants of at least 10 ¹⁷ cm ^-3 and a thickness of at least 0.1 μm and AlGaAs layer 6 with a difference a concentration of acceptor and donor alloying impurities of not less than 3 · 10 ¹⁷ cm ^-3 and a thickness of not less than 0.1 microns;

Figure 1 shows the known solution of the prototype [1], which shows the distribution profiles of the doping acceptor and donor impurities in the GaAs p-i-n structure, which shows:

- single-crystal heavily doped GaAs substrate of 1 p ⁺ conductivity type with an acceptor impurity concentration of 5 · 10 ¹⁹ cm ^-3 with a thickness of at least 300 μm;

- GaAs p-type epitaxial conductivity layer 2 with a varying acceptor impurity concentration from 5 · 10 ¹⁹ cm ^-3 to 10 ¹² cm ^-3 or less and having a thickness of at least 10 μm;

- pn-transition epitaxial GaAs i-layer 3 with a thickness of 3 ÷ 70 μm, containing a metallurgical transition, with a difference concentration of acceptor and donor dopants of not more than 10 ¹² cm ^-3 ;

- high-resistance GaAs epitaxial layer 4 of n-type conductivity with a varying concentration of donor and acceptor dopants from the concentration at the interface with the i-layer 3 to 10 ¹⁶ cm ^-3 and a thickness of at least 15 μm.

The essence of the invention is illustrated in Fig.2, 3, which shows the distribution of doping acceptor and donor impurities in p-i-n GaAs and p-i-n AlGaAs / GaAs structures. Figure 2, 3 shows the following:

- highly doped single-crystal GaAs substrate 1 with a differential concentration of acceptor and donor dopants of at least 3 · 10 ¹⁸ cm ^-3 ;

и толщиной не менее 5 мкм;- epitaxial GaAs layer 2 with a varying differential concentration of acceptor and donor dopants from the concentration in the high-alloy substrate to values less than or equal to

and a thickness of at least 5 microns;

;- pn conductive transition epitaxial GaAs i-layer 3 having a thickness of 5 ÷ 100 μm with a differential concentration of acceptor and donor dopants in the multi-epitaxial metallurgical transition zone is less than or equal to

;

- a highly doped epitaxial GaAs layer of n ⁺ type 5 with a difference concentration of acceptor and donor dopants in the surface layer of at least 10 ¹⁷ cm ^-3 and a thickness of at least 0.1 μm;

- a highly doped heteroepitaxial AlGaAs layer of 6 n ⁺ type conductivity with a differential concentration of acceptor and donor dopants of at least 3 · 10 ¹⁷ cm ^-3 and a thickness of at least 0.1 μm.

The concentration of the dopant acceptor impurity of Zn atoms in a single-crystal substrate has a decisive influence on the density of defects on the surface of the initial GaAs p ⁺ type substrate, the higher the concentration of dopant, the higher the density of defects, the higher the probability of transferring these defects during epitaxial growth to the epitaxial pin of GaAs , AlGaAs structures, therefore, in the substrate, it is necessary to reduce the doping level of the acceptor impurity to a level much lower than 5 · 10 ¹⁹ cm ^-3 . This favorably affects the growth of the p-type conductivity layer, the concentration of impurities in which is easier to control, to control the process of suppressing defects in the p-layer.

. Данный слой получается за счет сложных технологических приемов во время жидкостной эпитаксии с использованием амфотерных свойств легирующих атомов кремния (Si).The decisive role in pin GaAs, AlGaAs / GaAs structures is played by the pn transition i-layer (physical pn junction) containing the space charge region and the internal multimetallic transition with a difference concentration of acceptor and donor impurities of less than or equal to

. This layer is obtained due to complex technological methods during liquid epitaxy using the amphoteric properties of doping silicon atoms (Si).

The uniqueness of the i-layer is as follows:

- through it, the injection of carriers is rather efficient;

- it has high electric strength exceeding 3 · 10 ⁵ V / cm (~ 30 V / μm);

- due to the provision of a large physical p-n junction width, the capacitance decreases sharply, 20–30 times, compared with silicon, silicon-carbide p-n or barrier junctions;

- increases frequency and dynamic properties.

The exception of the n-type GaAs conductivity of the high-resistance layer is aimed at increasing the speed and current density of the generated p ⁺ -in ⁺ structure, since large values of the accumulation charge accumulate during the direct current flow due to the high density of minority carriers in the high-resistance n-type layer (base) current, in this case, holes, and this increases the recovery time of the reverse current and, therefore, affects the dynamics of the diode.

Thus, in the present invention, the design of the diode takes the form of a p ⁺ -in ⁺ structure without using the traditional high-resistance base region of diode structures, in particular silicon. As a result of this, the p ⁺ and n ⁺ regions of the new diode design are capable of injecting holes and electrons into the i-transition region, respectively, i.e. charge carriers. In the i-zone, holes and electrons injected from the anode and cathode regions simultaneously appear with an nonequilibrium concentration of carriers forming a high density and high conductivity electron-hole plasma, as a result of this, the density of the forward biased current increases and there is no growth component of the direct voltage drop due to the high-resistance n- type of base.

Such a two-injection diode is a new solution or modification of the well-known Shockley model of the pn junction, in fact it is a p ⁺ -n ⁺ high-voltage diode containing a physical pn junction in the form of an i-region, with the absence of a generally accepted (classical) high-resistance base in the diode structure.

Electrons are injected from the cathode region of the diode either from an n ⁺ -GaAs layer, or from an n ⁺ -AlGaAs layer, or a combination of a buffer GaAs layer (i.e., a layer protecting the transition hetero-region from the electric field at high voltages, but allowing efficient injection from the heterolayer) and the n ⁺ -AlGaAs layer, which, due to the larger band gap, provides more efficient injection of electrons through the buffer layer or directly into the i-region, or a combination of the n ⁺ type GaAs, AlGaAs and GaAs successive layers is possible to reduction of mechanical stresses, providing high heteroeffective injection of electrons into the i-region and making reliable ohmic contact to the surface GaAs n ⁺ epitaxial layer.

The concentrations of dopants in the cathodic n ⁺ regions in each case are selected experimentally.

In the process of switching the current in the p ⁺ -in ⁺ reduced structure from direct to reverse (applying a reverse voltage), in contrast to the traditional diode structure with a high-resistance base, the mechanism of switching and resorption of the accumulated charge in the i-region (electron-hole plasma) becomes predominantly drift-diffusion, rather than diffusion-drift, as, for example, in conventional silicon high-voltage fast-recovery diodes, i.e. Carriers are extracted by an applied electric field - holes into the anode (p-band), electrons - into the cathode (n-band), with simultaneous recombination at deep levels. This mechanism of resorption of the accumulated charge in the electron-hole plasma has a decisive influence on the frequency properties and dynamics of the proposed new design of diodes ("baseless" design of the diode crystal).

According to the above design, experimental samples were obtained:

one). p ⁺ -in ⁺ GaAs diodes with an n ⁺ GaAs cathode up to 3.0 μm thick and a donor impurity concentration of 1 · 10 ¹⁸ cm ^-3 , with a forward voltage U _F ≤1.2 V at a forward current I _F = 3 A, s reverse breakdown voltages U _RRM ≥920 V (with an i-layer thickness of about 50 μm) and recovery time when switching from open to closed (non-conducting) state τ _rr <30 nsec. At di / dt = 200 A / μs U _RRM = 200 V;

2). Experimental samples of p ⁺ -in ⁺ / n ⁺ AlGaAs / GaAs diodes with an n ⁺ -n ⁺ type cathode made on the basis of successive epitaxial layers of n ⁺ -GaAs and n ⁺ -AlGaAs, on which direct voltage drops are obtained by 0.15 lower ÷ 0.2 V than in the p ⁺ -in ⁺ diode design on monoepitaxial GaAs.

A specific example of the implementation of p ⁺ -in ⁺ diode structures is as follows:

On the initial GaAs, a single-crystal substrate with a thickness of 300 μm, ⌀ 50.6 mm, doped with Zn to a concentration of 1 · 10 ¹⁹ cm ^-3 , in a single technological process of liquid-phase epitaxy in a quartz reactor from a solution of GaAs in Ga from the gap between two p ⁺ GaAs substrates, doped with Zn (with N _A > 10 ¹⁹ cm ^-3 ) in a forced-flow H ₂ stream, a p-layer 2, an i-transition layer 3, an n-high-voltage region 4, a highly doped n ⁺ GaAs region 5 were grown sequentially. The obtained epitaxial pin the structure has metallurgical transitions inside the i-epitaxial region ty 3. The processes of liquid epitaxy were carried out at a relatively low temperature of ~ 950 ° C. The diffusion length of electrons L _n was measured on test p ⁺ -p-n ⁺ structures with a differential concentration of acceptor and donor impurities ranging from 10 ¹⁴ to 10 ¹⁷ cm ^-3 . The distribution profile of donor and acceptor impurities was determined by CV using the characteristics of the pn junction, as well as on oblique thin section installations.

The lifetime of nonequilibrium hole carriers was determined by the photoresponse. The values of L _p and τ _p were established depending on the difference concentration of donor and acceptor impurities, as well as the dependence of τ _p and L _p on the injection level and the density of the introduced charge.

In the case of creating the AlGaAs heterostructure, the same liquid epitaxy method was used with the epitaxial layer growing from arsenic melt in gallium with the addition of aluminum using tellurium (Te) or tin (Sn) dopants at temperatures 120-150 ° C lower than during the creation epitaxial pin structure.

Taking into account the segregation coefficient of impurities of the above alloying additives, a three-stage temperature gradient of recrystallization of the epitaxial layer from an Al _x Ga _1-x As liquid solution is set to ensure a high prevalence of the donor impurity over the acceptor one.

Claims (2)

1. A multi-epitaxial crystal structure of a two-injection high-voltage hyperfast recovery diode based on gallium and arsenic compounds, containing a highly doped single-crystal p ⁺ type conductivity substrate, an p ^- type epitaxial GaAs layer made on it, a pn-type conductivity pn-transition layer containing an epitaxial GaAs i-type epitaxial GaAs i-layer the space charge region and the intra-located multi-epitaxial metallurgical transition zone, the epitaxial GaAs layer made on the pn-transition i- epitaxial layer, characterized in that:
- a highly doped single-crystal GaAs substrate of p ⁺ type conductivity is performed with a differential concentration of acceptor and donor dopants of at least 3 × 10 ¹⁸ cm ^-3 and a thickness of at least 200 μm;
- the p-type epitaxial layer is performed with a thickness of at least 5.0 μm and a varying difference concentration of donor and acceptor dopants from the concentration in the single-crystal p ⁺ type conductivity of the GaAs substrate to values no more than

;
- pn conductive transition epitaxial GaAs i-layer containing a space-charge region and an intra-located multi-epitaxial metallurgical transition zone is performed with a difference concentration of acceptor and donor dopants of less than or equal to

and a thickness of 5 ÷ 100 microns;
- the epitaxial GaAs layer on the pn transition epitaxial i-layer is made of highly doped n ⁺ -type conductivity with a differential concentration of acceptor and donor dopants in the surface layer of at least 1 · 10 ¹⁷ cm ^-3 and a thickness of at least 0.1 μm. 2. Multiepitaksialnaya crystal structure dvuhinzhektsionnogo high giperbystrovosstanavlivayuschegosya diodes based on gallium and arsenic compounds according to claim 1, characterized in that high-alloy on the surface of the epitaxial GaAs layer n ⁺ -type conductivity performed highly doped epitaxial layer of AlGaAs n ⁺ type conductivity with a concentration difference of the donor and acceptor impurities of not less than 3 · 10 ¹⁷ cm ^-3 and a thickness of not less than 0.1 microns.

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