Technical background
Elgin-Kidde at first is used in the power supply supply side with β-Voltaic Effect in nineteen fifty-seven, and successfully experiment produces first radioisotope micro battery (β-Voltaic Battery).Since 1989, GaN, GaP, AlGaAs, materials such as polysilicon are utilized the material as β-Voltaic battery in succession.Along with the preparation of semiconductor material with wide forbidden band SiC and the progress of technology, 2006 begin, and have occurred the relevant report of SiC base isotope battery in the world in succession.
Document " APPLIED PHYSICS LETTERS 88; 064101 (2006) " Demonstration of atadiation resistant; hight efficiency SiC betavoltaic " " has been introduced the C.J.Eiting by New Mexico Qynergy Corporation; V.Krishnamoorthy; AndS.Rodgers; People such as the J.David Roberston and JohnBrockman of T.George and U.S. Colombia University of Missouri have proposed silit p-i-n eliminant nuclear battery jointly, and are as shown in Figure 7, and this p-i-n eliminant nuclear battery comprises the highly doped SiC substrate of the highly doped SiC layer of radioactive isotope power supply 3, p type ohmic contact layer 12, p type 9, p type SiC layer 11, intrinsic i layer 10, n 6, Ohm contact electrode 7 from top to bottom successively.
Document " APPLIED PHYSICS LETTERS 88; 033506 (2006) " Demonstration of a 4HSiC betavoltaic cell " " has been introduced the M.V.S.Chandrashekhar by USA New York Cornell university; C.I.Tomas; Hui Li; People such as M.G.Spencer and Amit Lal have proposed silit pn eliminant nuclear battery, and are as shown in Figure 8, and this pn eliminant nuclear battery comprises the low-doped SiC layer of the highly doped SiC layer of radioactive isotope power supply 3, Ohm contact electrode 7, n type 14, p type 8, the highly doped SiC layer 9 of p type and p type ohmic contact layer 12 from top to bottom successively.
Disclose by Zhang Lin among the Chinese patent CN 101325093A, the Schottky junction type nuclear cell that people such as Guo Hui propose based on SiC, as shown in Figure 9, this Schottky junction type nuclear cell comprises bonded layer 1, schottky metal layer 13, SiO from top to bottom successively
2The highly doped SiC substrate of the low-doped SiC epitaxial loayer of passivation layer 4, n type 5, n type 6, Ohm contact electrode 7.
But the processes of SiC material is difficulty relatively.When preparation SiC PN junction; Generally be to adopt the low-doped n type layer of isoepitaxial growth; Afterwards again with homoepitaxy or particle implantttion technique at the highly doped p type layer of surface preparation one deck, all there are certain defective in this silit PN junction and PIN nucleus battery on technology and structure.Often doping content is not high to adopt homoepitaxy to prepare P type layer, in to build electromotive force corresponding lower, and bring difficulty can for the preparation of p type Ohmic contact; Adopt ion injection method to form p type layer process more complicated, and can cause surface damage the activated at process of implanted dopant, the enhanced surface complex effect, the leakage current of increasing device influences battery behavior.Structurally have only the living charge carrier of irradiation that depletion region is interior and a near minority diffusion length is interior to be collected.In this PN junction structure; In order to prevent that Ohm contact electrode from stopping incident particle; Must be with a corner of Ohmic electrode overcurrent device, but can make like this from Ohmic electrode irradiation far away give birth to charge carrier in transport process by compound, and incident particle must pass the SiO on surface
2Passivation layer and part P type layer cause energy loss, reduce energy conversion efficiency.
The disclosed nuclear battery of Chinese patent CN 101325093A adopts the schottky junction structure, has avoided above-mentioned PN junction technology to realize difficult problem, but this schottky junction nuclear battery schottky contact layer covers the entire cell zone; As shown in Figure 8; Because incident particle all can receive stopping of schottky contact layer after arriving device surface, has only the part particle can get into device inside; And the particle that gets into depletion region just can have contribution to the output power of battery; Therefore, the loss of the nuclear battery projectile energy of this structure is big, and energy conversion efficiency is lower.
Summary of the invention
The objective of the invention is to avoid the deficiency of above-mentioned prior art, propose fingered schottky contact nuclear battery based on silit and preparation method thereof,, improve energy conversion efficiency to reduce the projectile energy loss.
For realizing above-mentioned purpose, fingered schottky contact minisize nuclear battery provided by the invention comprises successively that from top to bottom bonded layer, radioactive isotope power supply layer, schottky contact layer, doping content are 1 * 10
15~5 * 10
15Cm
-3The low-doped SiC epitaxial loayer of n type, doping content be 5 * 10
17~5 * 10
18Cm
-3Highly doped SiC substrate of n type and Ohm contact electrode, the radioactive isotope power supply layer around be SiO
2Passivation layer; Wherein, schottky contact layer is equidistant dactylitic texture, and this dactylitic texture is made up of with the vertical finger of m bar a horizontal finger; M>=3; The vertical finger of m bar is positioned at the same side of horizontal finger, and the radioactive isotope power supply layer covers on the low-doped SiC epitaxial loayer between vertical finger of fingered schottky contact layer and the vertical finger, and bonded layer is positioned on the horizontal finger of fingered schottky contact layer.
Described fingered schottky contact layer is translucent, and thickness is smaller or equal to 20nm.
Described vertical finger spacing:
Guarantee that depletion region can cover the entire cell zone, wherein, W is the schottky junction width of depletion region, and ε is the silit specific inductive capacity, and e is an electron charge, V
BiBe the interior electric potential difference of building, N
dBe low-doped outer layer doping concentration.
The width H of described horizontal finger is a a times of vertical finger width h, 2≤a≤15; The length L of horizontal finger is b a times of vertical finger length R, 1≤b≤20.
For realizing above-mentioned purpose, the method for making of fingered schottky eliminant minisize nuclear battery provided by the invention comprises the steps:
(1) be 5 * 10 in doping content
17~5 * 10
18Cm
-3The epitaxial surface of the highly doped n type of SiC SiC substrate on grow doping concentration be 1 * 10
15~5 * 10
15Cm
-3Low-doped n type epitaxial loayer;
(2) described epitaxial loayer is carried out dry-oxygen oxidation, form SiO
2Passivation layer;
(3) with the reactive ion etching method at the back-etching SiC of substrate layer, electron beam evaporation Ni/Cr/Au metal level, under 1100 ± 50 ℃ of temperature, annealing forms Ohmic contact in the nitrogen atmosphere;
(4) at SiO
2Gluing on the passivation layer, the photoetching making restraining barrier, using concentration is that 5% HF acid corrosion was windowed in 10 seconds;
(5) at the substrate face gluing; Use the photolithography plate of band dactylitic texture shape; Make the finger-like figure by lithography, the translucent high barrier schottky metal Ni of deposit or Pt or Au peel off the fingered schottky contact layer that formation is made up of a vertical finger with at least 3 of horizontal finger through ultrasound wave;
(6) at the substrate face gluing, photoetching is windowed directly over the horizontal finger of schottky contact layer, electron beam evaporation Cr/Au, and peel off the formation bonded layer through ultrasound wave;
(7) on each vertical finger and the epitaxial loayer between the vertical finger of schottky contact layer, plate radioactive isotope power supply Ni-63 layer.
The present invention compared with prior art has following advantage:
1) the present invention is owing to adopt silicon carbide-based schottky junction structure, rather than p-n junction or p-i-n structure, and technology is simple, is easy to realize.
2) the present invention is owing to adopt translucent high barrier schottky metal level, not only improved the nuclear battery open-circuit voltage but also effectively reduced metal level to the stopping of low energy incident particle, the energy conversion efficiency of nuclear battery is obviously improved.
3) the present invention adopts the fingered schottky contact but not all standing formula Schottky contacts, and incident particle can not pass schottky metal layer greatly, but directly gets into depletion region, has further improved the energy conversion efficiency of nuclear battery.
Embodiment
With reference to Fig. 1, Fig. 2 and Fig. 3, it is 5 * 10 that nuclear battery of the present invention adopts doping content
17~5 * 10
18Cm
-3The highly doped n type of
SiC SiC substrate 6; Be that one deck doping content is 1 * 10 above the substrate
15~5 * 10
15Cm
-3The low-doped
epitaxial loayer 5 of n type;
Substrate 6 back sides are respectively the
Ohm contact electrode 7 that the Ni/Cr/Au of 200/50/200nm forms by thickness; Be fingered
schottky contact layer 2 on the low-doped
epitaxial loayer 5 of n type, as shown in Figure 5, this fingered schottky contact layer thickness is smaller or equal to 20nm; Form with the vertical finger of m bar by a horizontal finger, m>=3, the vertical finger of m bar is distributed in the same side of horizontal finger; The width H of horizontal finger is a a times of vertical finger width h, 2≤a≤15, and the length L of horizontal finger is b a times of vertical finger length R; 1≤b≤20, vertical finger spacing:
Wherein, W is the schottky junction width of depletion region, and ε is the silit specific inductive capacity, and e is an electron charge, V
BiBe the interior electric potential difference of building, N
dBe low-doped outer layer doping concentration; On the low-doped silicon carbide epitaxial layers between vertical finger of finger-like contact layer and the vertical finger is radioactive isotope
power supply layer 3; The bonded layer of forming by Cr/Au above the
horizontal finger 1, as shown in Figure 4; Around the
radioactive isotope layer 3 is SiO
2Passivation layer 4.
With reference to Fig. 6, method for making of the present invention is through following embodiment explanation.
Embodiment 1
In the 1st step, the low-doped n type of extension epitaxial loayer on the highly doped n type of the SiC substrate is like Fig. 6 a.
Selecting doping content for use is 5 * 10
18Cm
-3The highly doped n type of SiC SiC substrate make substrate 6, after the cleaning, using low pressure hot wall chemical vapor deposition method growth thickness on epitaxial surface to be about 3 μ m doping contents is 5 * 10
15Cm
-3The low-doped epitaxial loayer 5 of 4H-SiC, its epitaxial temperature is 1570 ℃, pressure 100mbar, reacting gas are silane and propane, carrier gas is a pure hydrogen.
In the 2nd step, on epitaxial loayer, form SiO
2Passivation layer is like Fig. 6 b.
Under 1100 ± 50 ℃ of temperature, the substrate sample of externally delaying is carried out two hours dry-oxygen oxidation, forms SiO
2Passivation layer.
In the 3rd step, form Ohmic contact at substrate back, like Fig. 6 c.
(3.1) using the reactive ion etching method is the SiC layer of 0.5 μ m at the back-etching thickness of substrate 6;
(3.2) 6 back side deposited by electron beam evaporation thickness of the substrate after etching are respectively the Ni/Cr/Au of 200/50/200nm;
(3.3) under 1100 ± 50 ℃ of temperature, in the nitrogen atmosphere sample annealing was formed Ohm contact electrode 7 in 2 minutes.
The 4th step is at SiO
2Gluing on the passivation layer, window with the HF acid corrosion in the photoetching making restraining barrier, like Fig. 6 d.
(4.1) at SiO
2Spin coating photoresist on the passivation layer;
(4.2) photoetching making restraining barrier;
(4.3) using concentration is 5% buffered HF acid corrosion 10 seconds, at SiO
2Etch the effective coverage of battery in the passivation layer 4.
In the 5th step,, use the photolithography plate of band dactylitic texture shape at the substrate face gluing; Make the finger-like figure by lithography; The translucent high barrier schottky metal Ni of deposit peels off the fingered schottky contact layer that formation is made up of a horizontal finger and 3 vertical fingers through ultrasound wave, like Fig. 6 e.
In the 6th step, at the substrate face gluing, photoetching is windowed directly over the horizontal finger of schottky contact layer, electron beam evaporation Cr/Au, and peel off the formation bonded layer through ultrasound wave, like Fig. 6 f.
In the 7th step, on each vertical finger and the epitaxial loayer between the vertical finger of schottky contact layer, electroplate radioactive isotope power supply Ni-63 layer, like Fig. 6 g.
Embodiment 2
The first step, the low-doped n type of extension epitaxial loayer on the highly doped n type of the SiC substrate.
Selecting doping content for use is 1 * 10
18Cm
-3The highly doped n type of SiC SiC substrate make substrate 6, after the cleaning, using low pressure hot wall chemical vapor deposition method growth thickness on epitaxial surface to be about 3 μ m doping contents is 3 * 10
15Cm
-3The low-doped epitaxial loayer 5 of 4H-SiC, its epitaxial temperature is 1570 ℃, pressure 100mbar, reacting gas are silane and propane, carrier gas is a pure hydrogen.
In second step, on epitaxial loayer, form SiO
2Passivation layer.
Under 1100 ± 50 ℃ of temperature, the substrate sample of externally delaying is carried out two hours dry-oxygen oxidation, forms SiO
2Passivation layer.
In the 3rd step, form Ohmic contact at substrate back.
(3.1) using the reactive ion etching method is the SiC layer of 0.5 μ m at the back-etching thickness of substrate 6;
(3.2) 6 back side deposited by electron beam evaporation thickness of the substrate after etching are respectively the Ni/Cr/Au of 200/50/200nm;
(3.3) under 1100 ± 50 ℃ of temperature, in the nitrogen atmosphere sample annealing was formed Ohm contact electrode 7 in 2 minutes.
The 4th step is at SiO
2Gluing on the passivation layer, window with the HF acid corrosion in the photoetching making restraining barrier.
(4.1) at SiO
2Spin coating photoresist on the passivation layer;
(4.2) photoetching making restraining barrier;
(4.3) using concentration is 5% buffered HF acid corrosion 10 seconds, at SiO
2Etch the effective coverage of battery in the passivation layer 4.
The 5th step; At the substrate face gluing, use the photolithography plate of band dactylitic texture shape, make the finger-like figure by lithography; The translucent high barrier schottky metal Pt of deposit peels off the fingered schottky contact layer that formation is made up of a horizontal finger and 20 vertical fingers through ultrasound wave.
In the 6th step, at the substrate face gluing, photoetching is windowed directly over the horizontal finger of schottky contact layer, electron beam evaporation Cr/Au, and peel off the formation bonded layer through ultrasound wave.
The 7th step, on the epitaxial loayer between vertical finger of each of schottky contact layer and the vertical finger, electroless plating radioactive isotope power supply Ni-63 layer.
Embodiment 3
The A step, the low-doped n type of extension epitaxial loayer on the highly doped n type of the SiC substrate.
Selecting doping content for use is 5 * 10
17Cm
-3The highly doped n type of SiC SiC substrate make substrate 6, after the cleaning, using low pressure hot wall chemical vapor deposition method growth thickness on epitaxial surface to be about 3 μ m doping contents is 1 * 10
15Cm
-3The low-doped epitaxial loayer 5 of 4H-SiC, its epitaxial temperature is 1570 ℃, pressure 100mbar, reacting gas are silane and propane, carrier gas is a pure hydrogen.
In the B step, on epitaxial loayer, form SiO
2Passivation layer.
Under 1100 ± 50 ℃ of temperature, the sample of externally delaying carries out two hours dry-oxygen oxidation, forms SiO
2Passivation layer.
In the C step, form Ohmic contact at substrate back.
(C1) using the reactive ion etching method is the SiC layer of 0.5 μ m at the back-etching thickness of substrate 6;
(C2) 6 back side deposited by electron beam evaporation thickness of the substrate after etching are respectively the Ni/Cr/Au of 200/50/200nm;
(C3) under 1100 ± 50 ℃ of temperature, in the nitrogen atmosphere sample annealing was formed Ohm contact electrode 7 in 2 minutes.
The D step is at SiO
2Gluing on the passivation layer, window with the HF acid corrosion in the photoetching making restraining barrier.
(D1) at SiO
2Spin coating photoresist on the passivation layer;
(D2) photoetching making restraining barrier;
(D3) using concentration is 5% buffered HF acid corrosion 10 seconds, at SiO
2Etch the effective coverage of battery in the passivation layer 4.
The E step; At the substrate face gluing, use the photolithography plate of band dactylitic texture shape, make the finger-like figure by lithography; The translucent high barrier schottky metal Cu of deposit peels off the fingered schottky contact layer that formation is made up of a horizontal finger and 60 vertical fingers through ultrasound wave.
F step, at the substrate face gluing, photoetching is windowed directly over the horizontal finger of schottky contact layer, electron beam evaporation Cr/Au, and peel off the formation bonded layer through ultrasound wave.
The G step, on the epitaxial loayer between vertical finger of each of schottky contact layer and the vertical finger, molecular plating radioactive isotope power supply Ni-63 layer.
The foregoing description does not constitute the vertical finger number in any restriction of the present invention, particularly fingered schottky layer, needs to confirm according to the practical application desired output power.