RU2791861C1 - Crystal of a monopolar-bipolar power high-voltage hypervelocity gallium arsenide diode with heterojunctions, with photonic and photovoltaic properties - Google Patents

Abstract

FIELD: semiconductor devices.

SUBSTANCE: crystal of a monopolar-bipolar power high-voltage hypervelocity gallium arsenide diode with heterojunctions, with photonic and photovoltaic properties includes a single-crystal GaAs substrate of n⁺-type conductivity with epitaxial layers successively made on it: a GaAs buffer layer of n⁺-type conductivity, Al_xGa₁ layer _-x As of n⁺-type conductivity with x = 0.25 ÷ 0.6, GaAs layer of p⁺-type conductivity, Al_xGa_1-xAs layer of p⁺-type conductivity with x = 0.25÷ 0.6, GaAs layer of p⁺-type conductivity, and ohmic contacts on the surface of the epitaxial GaAs layer of p⁺-type conductivity and on the back surface of the single-crystal GaAs substrate n⁺-type conductivity. Inside the heterogeneous volume of AlGaAs - GaAs of p⁺-type conductivity, on the surface of the GaAs layer of p-type conductivity, local epitaxial GaAs layers of n⁺-type conductivity are made, electrically connected with GaAs - AlGaAs layers of p⁺-type conductivity. Inside the heterogeneous volume of AlGaAs - GaAs of p⁺-type conductivity, on the surface of the GaAs layer of p-type conductivity, local Schottky barriers are made, electrically connected with GaAs - AlGaAs layers of p⁺-type conductivity. To passivate the surface charge, nanometer ALD films of aluminium oxide and nitride are deposited on the side surface of the crystal.

EFFECT: reduction of forward voltages, capacitive parasitics and reverse recovery time of diodes; increase of the operating temperatures of the monopolar-bipolar diode crystal and reduction of parasitic leakage currents; increase of the dynamic stability of diode structures in the mode of hard resonant switching at high values of di/dt and dU/dt; to implement the concept of a power hypervelocity high-voltage diode, LED up to volume coherent radiation with a strong inversion of photovoltaic diode charge carriers.

4 cl, 6 dwg

Description

Technical field

The invention relates to the field of semiconductor devices, in particular, to high-voltage power bipolar diodes p-i-n type, with a short recovery time of reverse resistance.

State of the art

High-voltage power ultrafast (UFRED according to Western classification) and hyperfast (HyperFRED) diodes for energy-dense VIP and IPM are mainly made on silicon (Si) substrates, with switching frequencies from hundreds of kilohertz to several megahertz. For example, HyperFRED LXA06B600 from Power Integrations (U _R = 600 V; I _F = 6 ÷ 20 A; τ _rr = 23 ns/25°C). For reverse voltages up to 200 V, silicon Schottky diodes (SBD according to Western classification) are widely used, for tens of amperes and τ _rr = 20 ns manufactured by Vishay (USA). Also, for various purposes, diodes based on silicon carbide SiC SBD / JBS with U _R = 650 are widely used; 1200 and 1700 V, τ _rr = 15 ÷ 30 ns, I _F up to 50 A produced by Cree (USA) and Infineon (Germany).

The sector of high-voltage GaAs power diodes on the world market is represented by GaAs Schottky diodes (GaAs SBD) of the DGSS6-06CC series by IXYS (part of Littelfuse, USA) and Semelab (part of TT-Elelectronics, UK), made according to MOCVD epitaxial technology, for limited maximum reverse operating voltages (U _RRM ) up to 250 ÷ 300 V, having currents up to 15 A and recovery times τ _rr up to 20 ns/25°С.

All of the above classes of high-speed power high-voltage diodes have serious limitations in terms of operating temperature (+125°C), switching frequency, including 600 ÷ 650 - volt SiC SBD (due to the extra high capacitance in the speed formula τ = RC), which is limited at best 5 ÷ 10 MHz on the example of SiC SBD from Cree (USA), Infineon (Germany) and Si HyperFRED from the LXA06B600 series from Power Integrations (USA).

For GaN p-i-n and SBD (HyperFRED), only a cautious prediction can be made so far, and they are expected to be weaker in electrophysical parameters compared to diodes such as SiC SBD.

In Russia and Germany, a number of companies have developed hyper-speed GaAs high-voltage diodes with an operating temperature doubled compared to Si, SiC diodes, as evidenced by the patents of the Russian Federation:

- patent RU No. 2472249 dated December 31, 2009 "Crystal of an ultrafast high-voltage high-current gallium arsenide diode", authors Voitovich V.E., Gordeev A.I., Dumanevich A.N.;

- patent RU No. 2488911 dated July 27, 2013 "Method of manufacturing a semiconductor p-i-n structure based on GaAs-GaAlAs compounds by liquid epitaxy", authors Kryukov V.L., Kryukov E.V., Meerovich L.A., Strelchenko S. S., Titivkin K.A.; and others;

There are EC patents of the company “3-5 Power Electronics GmbH” (Germany) on GaAs p-i-n hyperspeed diodes. This is an exceptionally strong class of hyperfast high-voltage radiation-resistant diodes with a conversion frequency range from 2÷3 MHz (1200 volt p-i-n GaAs diodes) to 10 MHz (600 volt p-i-n GaAs diodes) with operating temperature up to +250°С.

But more high-frequency characteristics of high-voltage GaAs diodes (in particular, up to 600 ÷ 800 V) with twice the switching frequencies compared to p-i-n HyperFRED GaAs are needed.

In this regard, attention is drawn to new design options and technologies for the execution of hyperspeed diodes on GaAs single-crystal substrates, in particular, a combined isotype-bipolar (unipolar-bipolar) design with currently unthinkable recovery times and superdense electron-hole plasma (EHP) in a high-resistance conducting zone of the diode structure up to the negative differential resistance of the direct I–V characteristic (DOS on the direct I–V characteristic), i.e. with the achievement of values of direct voltage drop U _F (V), competitive with Schottky diodes, as well as with the properties of electroluminescence and photodetector of solar radiation.

From the analysis of foreign and domestic sources of scientific and technical information, GaAs diodes with heterojunctions, shown in publications [1], [2], with operating voltages of several hundred volts and currents higher than 10 ³ A / cm ² (note that a copper wire with a square section S \u003d 1.0 cm ² 1.0 m long at best can provide electrical current conductivity up to 300 A). This design of a unipolar-bipolar superpower high-voltage diode is taken as the closest prototype.

The crystal of such a gallium arsenide diode contains a cathode region from a single-crystal substrate GaAs n ⁺ -type conductivity with a donor impurity concentration of 2⋅10 ¹⁸ cm ^-3 with successive GaAsP n ⁺ -type heterojunction, n-type GaAs layer and p ⁺ -type GaAsP heterojunction as the anode.

The band diagram and structure of the prototype crystal are shown in FIG. 1, Fig. 2. (from the book [1]).

This solution, despite the ultra-high density and the presence of photon phenomena in the red spectrum of radiation and DOS on the direct CVC, still has limited technological capabilities to provide a wide range of reverse (blocking) operating voltages and, most importantly, due to the presence of phosphorus atoms in the heterosystem n ⁺ and p ⁺ - GaAsP, the mobility of "heavy" electrons and holes injected into the bipolar p ⁺ -n heterojunction and the unipolar (isotype) n ⁺ -n heterojunction with an energy of 0.3 eV higher than in the monoepitaxial n-type layer decreases sharply GaAs. In addition, phosphorus atoms at molarity x > 0.15 introduce tensorelectrophysical stresses in solid solutions of GaAs and phosphorus.

Due to a sharp decrease in the mobility of electrons and holes in the n-GaAs layer, the recovery time of the reverse resistance increases (up to 200 nanoseconds), which limits the possibility of using heterophase GaAsP diodes in RF conversion.

The essence of the invention

The technical task of the claimed invention is to expand the functionality.

The technical results achieved by the invention are:

- reduction of direct voltages, parasitic capacitances and reverse recovery times of diodes;

- increasing the operating temperature of the unipolar-bipolar diode crystal and reducing parasitic leakage currents;

- increasing the dynamic stability of diode structures in the mode of hard resonant switching at high values of di/dt and dU/dt;

- implementation of the concept of a power hyperspeed high-voltage diode + LED up to volumetric coherent radiation with a strong inversion of charge carriers + photovoltaic diode (solar photodetector).

To solve the problem and achieve the above results, we propose a crystal of a unipolar-bipolar power high-voltage hyperspeed gallium arsenide diode with heterojunctions, with photonic and photovoltaic properties, including a single-crystal GaAs substrate of n ⁺ -type conductivity with epitaxial layers successively made on it: a GaAs buffer layer n ⁺ - type of conductivity, layer of Al _x Ga _1-x As n ⁺ - type of conductivity with x = 0.25 ÷ 0.6, layer of GaAs of p-type conductivity, layer of Al _x Ga _1-x As p ⁺ - type of conductivity with x = 0.25 ÷ 0.6, a layer of GaAs p ^{+ -} type of conductivity, and ohmic contacts on the surface of the epitaxial layer GaAs p + - type of conductivity and on the back surface of a single-crystal GaAs substrate of n ⁺ - type conductivity.

Technical results are also achieved due to the fact that inside the heterophase volume of AlGaAs - GaAs p ⁺ -type conductivity, on the surface of the GaAs layer of p-type conductivity, local epitaxial layers of GaAs n ⁺ -type conductivity are made, electrically connected with GaAs - AlGaAs layers of p ⁺ -type conductivity.

Technical results are also achieved due to the fact that inside the heterophase volume of AlGaAs - GaAs p ⁺ -type conductivity on the surface of the GaAs layer of p-type conductivity, local Schottky barriers are made, electrically connected with GaAs - AlGaAs layers of p ⁺ -type conductivity.

Technical results are also achieved due to the fact that nanometer ALD films of aluminum oxide and nitride are deposited on the side surface of the crystal to passivate the surface charge.

Brief description of the drawings

Fig. 1 - Band structure of the crystal n-GaAs - n-GaAsP - n-GaAs - p-GaAsP (prototype structure).

Fig. 2 - Crystal structure of n-GaAs - n-GaAsP - n-GaAs - p-GaAsP (prototype structure).

Fig. 3 - Crystal structure of a unipolar-bipolar power high-voltage hyperspeed gallium arsenide diode with heterojunctions with photonic and photovoltaic properties.

Fig. 4 - The structure of a crystal with an epitaxial layer of GaAs n ⁺ -type conductivity inside the volume of the p ⁺ -AlGaAs layer on the surface of the p-GaAs layer.

Fig. 5 - Structure of a crystal with a Schottky barrier inside the volume of the p ⁺ -AlGaAs layer on the surface of the p-GaAs layer.

Fig. 6 - Graph of the distribution of the acceptor impurity in the p-GaAsP high-resistance region, obtained by the STM method.

Implementation of the invention

The essence of the proposed invention is illustrated in Fig. 3, Fig. 4, FIG. 5, which shows the crystal structure of a unipolar-bipolar power high-voltage hyperspeed gallium arsenide diode with heterojunctions with photonic and photovoltaic properties, containing a GaAs single-crystal substrate of n ⁺ -type conductivity (1), an epitaxial buffer GaAs layer of n ⁺ -type conductivity (2), epitaxial AlGaAs n ⁺ -layer (3), epitaxial GaAs layer of p-type conductivity (4), epitaxial AlGaAs heterolayer of p ⁺ -type conductivity (5), epitaxial GaAs layer of p ⁺ -type conductivity (6), as well as ohmic contacts ( 7), an epitaxial GaAs layer of the n ⁺ -type conductivity (8), a Schottky barrier (9) to the p-GaAs layer in the bulk of the AlGaAs/GaAs p ⁺ heterojunction.

Shown in FIG. 3, 4, 5, the GaAs crystal structure of a unipolar bipolar diode includes two series-connected barrier junctions with a common p-base, namely, a bipolar n ⁺ -p junction based on n ⁺ -GaAs layers (substrate) and p-GaAs ( epitaxial layer) and unipolar, i.e. p ⁺ -p type isotype heterojunction based on p ⁺ -AlGaAs - p-GaAs heterojunction. In this case, it is important to fulfill the condition that the thickness of the p-type GaAs layer must be less than or equal to three diffusion lengths L _n of electrons, as minority charge carriers in the p-GaAs region, and the concentration drop of the acceptor impurity in the isotype p ⁺ -p junction must be in within at least two to three orders of magnitude. In this case, it should be taken into account that there are no requirements for the mobility of charge carriers injected from the p ⁺ - heteroregion, and the time of their relaxation when switching the diode from a directly connected state to a closed state, i.e. the non-conducting state will be no worse than 10 ^-12 sec., which is shown in the monograph SMSze "Physics of Semiconductor Devices" in 2 volumes, 1981. As a result, the rate of change in the accumulated charge of the EHP in the p-region will be determined by the high-speed electron mobility in the p-GaAs region with almost ceiling, electron mobility (μ _n ) in pin/nip GaAs LPE junctions, reaching values up to μ _n = 7800 cm ² /V⋅sec, which is at least 1.8 times higher than in similar structures obtained by MOCVD - epitaxial method. As follows from the physics and principles of operation of bipolar pin / nip and isotype n ⁺ -n and p ⁺ -p type transitions, in the high-resistance region, a “light” mobile EHP plasma is formed from the position of ambipolar charge diffusion, the velocity of which is actually determined by the ratio μ _n to hole mobility μ _p , i.e. theoretically, the annihilation of the EHP charge in the p-region of the proposed invention, when the diode is turned off by the blocking voltage, will be determined by the rate of ambipolar diffusion/drift of the plasma EHP in the p-region, determined by the ratio μ _n /μ _p in GaAs, and not by the ratio μ _p /μ _n in pin GaAs diodes.

The calculated and experimental data on the values of τ _rr of the reduction charge show the values of τ _rr one and a half orders of magnitude lower than in pin GaAs structures.

Creation of n ⁺ epitaxial layers or Schottky barriers within the bulk of the p ⁺ -AlGaAs layer on the surface of the p-GaAs layer shown in FIG. 4, FIG. 5 will result in a dramatic reduction in diode reverse recovery times τ _rr compared to the basic chip design shown in FIG. 3.

The width W _p+-p of the p-region between the p ⁺ -AlGaAs/p ⁺ -GaAs regions acting as gates of the isotype TOC of a lean-gate field-effect transistor is calculated by the formula within:

,

,

and ϕ _T - is determined based on the formula:

,

,

where εε ₀ is the dielectric constant of GaAs;

q - electron charge (1.6 ⋅ 10 ^-19 C);

k - Boltzmann's constant;

T is the temperature in Kelvin;

N _p is the concentration of the acceptor impurity in the p region of GaAs;

N _p+ is the concentration of the acceptor impurity in the p ⁺ - AlGaAs heterolayer.

Shown in FIG. 3, the basic structure of a GaAs unipolar-bipolar crystal with a “transparent” AlGaAs/GaAs layer with a p ⁺ -type GaAs nanolayer on the surface of the p-layer is extremely photosensitive to the solar radiation spectrum and can reach an efficiency of up to a limit value of 28% due to the absence of recombination losses of hole charge carriers.

The structure in Fig. 5 with an inverse concentration of charge carriers in the valence band and the conduction band at high levels of injection of charge carriers of the isotype and bipolar pn transitions will emit powerful coherent radiation in the red region of the emission spectrum. Since the thickness of the p-layer can reach the level L _n in the p-layer ~ 50 ÷ 60 μm, this design of a unipolar-bipolar diode with heterojunctions provides a blocking voltage U _RRM up to 1200 V.

A specific example of the design of the crystal of a unipolar-bipolar high-voltage hyperspeed gallium arsenide diode with heterojunctions, proposed for the invention, with combined properties of hyperspeed current switching, electroluminescent properties, and at high current densities - properties of volumetric coherent radiation (laser radiation) in the red optical spectrum and a photodetector solar radiation with an efficiency close to 28% is given below:

An n ⁺ -GaAs buffer layer is deposited on a polished VGF - n ⁺ -GaAs LPE substrate, acting as a VGF-LPE transition epitaxial layer in order to sharply reduce the density of dislocations and nanocluster defects on the surface of the LPE n ⁺ -epitaxial GaAs layer to create the necessary LPE conditions epitaxy of n ⁺ -AlGaAs heterolayer with a molarity of aluminum atoms (Al) x = 0.25 ÷ 0.6, depending on the functional purpose of the newly created diode. In particular, when realizing the photonic properties of a diode crystal (LED/laser), the molarity is in the range x = 0.25 ÷ 0.35, which ensures the linearity of the zone-zone recombination processes in the p-region of GaAs.

One of the most important regions is the p-GaAs region, the experimental graph of the acceptor impurity profile of which is shown in Fig. 6.

The thickness of the p-layer ranges from 4 ÷ 10 µm - for a low-voltage 100 ÷ 250 V switching diode with photovoltaic properties and powerful volumetric coherent radiation - up to several tens of micrometers (in particular, up to L _{n max} = 60 µm) for a high-voltage version of a hyperspeed diode up to 1200 V.

The p ⁺ -AlGaAs heteroregion is made by the LPE method after preliminary CDP - polishing of the p-GaAs layer with a thickness of at least 3.0 μm, on the surface of which a pre-contact p ⁺ -GaAs layer with a thickness of at least 1.0 μm is grown by the MOCVD method.

The Schottky barrier transition is made from a titanium nanofilm, and the n ⁺ - region (0.5 ÷ 1.0 μm) of GaAs is made by the MOCVD method on the anodic p ⁺ -AlGaAs/p ⁺ -GaAs heterolayer. The n ⁺ -region is locally removed by precision etching through photolithographic windows. Ohmic contacts to the n ⁺ -cathode and p ⁺ -anode are deposited by the electron beam method. Au-Ge layers (up to 80 nm), a Ni layer (up to 100 nm thick) and an Au layer with a thickness of 2.0 µm were deposited.

To passivate the surface charge on the mesa bevel of the p ⁺ -pn ⁺ junction, ALD (Atom Layer Deposition) deposition of Al ₂ O ₃ + AlN nanofilms (total thickness no more than 15 nm) was used, followed by protection with photoimide.

High-voltage diode structures were obtained with U _R = 200–700 V, with τ _rr ≤ 5 nanoseconds/100°C in the nanosecond range in the mode U _R = 110 V; di/dt = 200 A/µs and I _F = 1.0 A, where: U _R - diode reverse voltage, di/dt - current decay rate, IF - forward current.

In the direct-on mode, a red glow of the diode structure was observed at high injection with the achievement of DOS on the direct CVC within the threshold values of the forward voltage of the diodes U _F ≤ 1.0 V.

The photovoltaic properties were evaluated under solar irradiation by comparing the dark characteristic of the direct CVC and under the action of solar irradiation.

In the ambient temperature range of 25 ÷ 100°C, active modulation of ΔV was observed on the direct CVC ranging from 0.2 V with extremely low (picoampere) dark current levels on the n ⁺ - p - p ⁺ - heterostructure.

LPE operations were carried out using specialized equipment with a quartz reactor and quartz equipment in a reducing gas transport medium at operating temperatures of 750 ÷ 900°C.

As mentioned earlier, as n ⁺ -GaAs substrates, VGF GaAs n ⁺ -type single-crystal substrates manufactured in Slovakia with a thickness of 350 ÷ 400 μm, with crystallographic orientation (111), diameters of 50.2 and 76 mm (two and three inches) were used.

Thus, the reduction in forward voltages, parasitic capacitances and reverse recovery times (one and a half orders of magnitude or more) of diodes compared with the prototype is achieved due to the greater mobility of electrons, which determines the speed ratio μ _n /μ _p , and not μ _p /μ _n (as in prototype), design elements, doping profile and the corresponding band diagram of the single crystal structure.

Increasing the operating temperature of the unipolar-bipolar diode crystal and

The reduction of parasitic leakage currents is achieved due to the improvement in the perfection of the crystal structure due to the exclusion of phosphorus, the use of GaAs LPE technologies, and also due to the passivation of the surface charge on the chamfer (side) of devices with nanometer ALD films.

Increasing the dynamic stability of diode structures in the mode of hard resonant switching at high values of di/dt and dU/dt, and exceeding the characteristics by half an order in terms of switching properties and conversion frequency compared to SiC Schottky diodes due to all the reasons listed above.

The proposed design of a hyperspeed power bipolar diode is intended for:

- HF resonant-contour VIP;

- HF IPM drive;

- Rectifying power take-off units of multiphase generators of aerospace vehicles with rotor speed up to 20,000 rpm;

- "Green" energy (voltage converters Solar inverters, wind power);

- Ultra-compact temperature-resistant RF IPM electrical modules and on-board VIPs;

- Converters for digital systems;

- Light engineering;

- Other uses.

Information sources:

[1] Zh.I. Alferov, V.M. Andreev, V.I. Korolkov, E.L. Portnoy, D.N. Tretyakov "Heterojunctions Al _x Ga _1-x As - GaAs", "Physics and Life". Ed. 2nd, add., Nauka Publishing House, St. Petersburg, 2001

[2] Zh.I. Alferov "On the possibility of creating a rectifier for ultrahigh current densities based on pin (pnn ⁺ , npp ⁺ ) structures with heterojunctions". FTP, 1, p. 436-438, 1967.

Claims (4)

1. A crystal of a unipolar-bipolar power high-voltage hyperspeed gallium arsenide diode with heterojunctions, with photonic and photovoltaic properties, including a single-crystal GaAs substrate of n ⁺ -type conductivity with epitaxial layers successively made on it: a GaAs buffer layer of n ⁺ -type conductivity, an Al layer _x Ga _1-x As n ⁺ -type conductivity with x = 0.25 ÷ 0.6, GaAs layer of p-type conductivity, Al _x Ga _1-x As p ⁺ -type conductivity with x = 0.25 ÷ 0 ,6, a layer of GaAs p ⁺ -type conductivity, and ohmic contacts on the surface of the epitaxial layer GaAs p+ -type conductivity and on the rear surface of the single-crystal GaAs substrate n ⁺ -type conductivity. 2. A crystal of a unipolar-bipolar power high-voltage hyperspeed gallium arsenide diode with heterojunctions with photonic and photovoltaic properties according to claim 1, characterized in that inside the heterophase volume of AlGaAs - GaAs p ⁺ -type conductivity, on the surface of the GaAs layer of p-type conductivity, local epitaxial GaAs layers of n ⁺ -type conductivity, electrically connected with GaAs - AlGaAs layers of p ⁺ -type conductivity. 3. A crystal of a unipolar-bipolar power high-voltage hyperspeed gallium arsenide diode with heterojunctions with photonic and photovoltaic properties according to claim 1, characterized in that inside the heterophase volume of AlGaAs - GaAs p ⁺ -type conductivity, on the surface of the GaAs layer of p-type conductivity, local Schottky barriers electrically coupled with GaAs - AlGaAs layers of p ⁺ -type conductivity. 4. A crystal of a unipolar-bipolar power high-voltage hyperspeed gallium arsenide diode with heterojunctions with photonic and photovoltaic properties according to claim 1, characterized in that nanometer ALD films of aluminum oxide and aluminum nitride are deposited on the side surface of the crystal to passivate the surface charge.

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