CN102064206A - Multi-component gradient-doping GaN UV (Ultraviolet) light cathode material structure and manufacture method thereof - Google Patents

Abstract

The present invention provides a reflective GaN ultraviolet photocathode material structure and its _{manufacturing} method _. crystal photoemission layer and Cs or Cs/O active layer; wherein, the unintentionally doped AlN buffer layer is grown on the substrate; the p-type Ga _x Al _1-x N multi-component mixed crystal photoemission layer is epitaxially grown on On the aforementioned AlN buffer layer; the Cs or Cs/O active layer is adsorbed on the front surface of the p-type _{GaxAl1 -xN} multi-component mixed crystal photoemission layer, and the thickness is on the order of nm. The structure adopts multi-component and gradient doping photoelectric emission layer, which increases the escape depth of photoexcited electrons in the emission layer, improves the probability of electron emission into vacuum in the emission layer, and thus improves the overall quantum efficiency of GaN UV photocathode , to obtain higher UV sensitivity.

Description

Multi-component, gradient doped GaN ultraviolet photocathode material structure and fabrication method

technical field

The invention belongs to the technical field of ultraviolet detection materials, and in particular relates to a reflective ultraviolet photocathode material structure and a manufacturing method based on the combination of semiconductor material epitaxy technology, semiconductor material doping technology and ultra-high vacuum surface activation technology.

Background technique

In recent years, with the improvement of GaN material preparation technology, p-type doping technology and the development of ultra-high vacuum technology, GaN UV photocathode is becoming a new type of high-performance UV photocathode. The surface of this cathode has negative electron affinity (Negative Electron Affinity, NEA), that is, the surface vacuum energy level of the cathode is lower than the bottom energy level of the conduction band in the body. Through emission into vacuum, there is no need for excess kinetic energy to overcome the potential barrier on the surface of the material, so that the escape probability of photo-excited electrons is greatly increased, and it is cold electron emission, so it has unique advantages such as high quantum efficiency, small dark emission, and concentrated energy distribution of emitted electrons. advantage. Its quantum efficiency is generally >24%, which is much higher than the 10% quantum efficiency of the traditional ultraviolet photocathode (such as cesium telluride, which has positron affinity, Positive Electron Affinity, PEA), and the band gap of GaN material is ~ 3.4eV, responding to ultraviolet radiation below 400nm, is a typical "sun-blind" material with good radiation resistance.

GaN UV photocathodes can be operated in reflective or transmissive mode. It operates in reflective mode when light is incident from the front surface of the cathode and electrons are also emitted from the front surface; in transmissive mode when light is incident from the back surface of the cathode and electrons are emitted from the front surface. The reflective GaN ultraviolet photocathode material structure generally includes a substrate material (usually sapphire), an AlN buffer layer epitaxially grown on the substrate, a p-type GaN photoemissive material grown on the buffer layer, and a low escape Activation layer for active element adsorption. The photoemissive layer is evenly doped with p-type. Due to the concentration difference between the surface of the emissive layer and the body, the electrons excited by the incident light from the valence band to the conduction band move to the body surface in the form of diffusion. During the transport process, some electrons are recombined after multiple collisions with the lattice and lose energy, and cannot escape, thereby reducing the number of electrons emitted, resulting in a low quantum efficiency of the cathode.

According to literature search, the use of variable doping structure photoemission layer can improve the transport ability of photoexcited electrons from the body to the body surface, increase the amount of electron escape, and thus obtain higher quantum efficiency. The photoemissive layer adopts an appropriate variable doping structure, which can generate a built-in electric field in the emissive layer body that is conducive to the movement of electrons to the surface, so that the electrons excited to the conduction band exist in the gap between the body and the body surface during the movement to the surface. The diffusion movement caused by the concentration difference can also perform drift movement under the action of the built-in electric field. The movement mode of diffusion and drift can increase the probability of electrons reaching the surface of the cathode, thereby increasing the probability of electrons escaping and improving the quantum efficiency. However, the proportion of photoexcited electrons escaped from the deeper part of the emissive layer is still small, and there is still room for improvement in the photoexcited electrons escape depth.

Contents of the invention

The technical problem to be solved by the present invention is to provide a multi-component, gradient doped GaN ultraviolet photocathode material structure and a manufacturing method for further improving the escape depth of photoexcited electrons.

The technical solution to realize the object of the present invention is: a multi-component, gradient doped GaN ultraviolet photocathode material structure, the material structure is successively substrate, unintentionally doped AlN buffer layer, p-type Ga _x Al _1-x N multi-component mixed crystal photoemission layer and Cs or Cs/O active layer.

A method for manufacturing a multi-component, gradient doped GaN ultraviolet photocathode material structure, comprising the following steps:

Step 1. On the upper surface of the double-sided polished sapphire substrate, grow an unintentionally doped AlN buffer layer through the epitaxial growth process of semiconductor materials;

Step 2, grow a p-type Ga _x Al _1-x N multi-component mixed crystal photoemission layer on the AlN buffer layer obtained in step 1 by epitaxial growth process and p-type doping process of III-V compound semiconductor materials as photoelectric emissive materials;

Step 3. Use chemical cleaning to remove the grease on the surface of the cathode material obtained in step 2 and the remaining inorganic attachments during processing; then send it into an ultra-high vacuum system to heat and purify the surface of the material to make the surface of the material reach atomic level cleanliness degree;

Step 4. Adsorb a single layer of Cs or multiple layers of Cs/O on the surface of the p-type GaN material through an activation process to form a Cs or Cs/O activation layer, and finally prepare a multi-component, gradient doped Heterostructure GaN UV photocathode.

Compared with the prior art, the present invention has significant advantages: 1) The present invention proposes a reflective ultraviolet photocathode material structure based on the combination of semiconductor material epitaxy technology, semiconductor material doping technology and ultra-high vacuum surface activation technology. The structure adopts Ga _x Al _1-x N multi-component and gradient doped photoemissive layer, which increases the escape depth of photo-excited electrons in the emissive layer and improves the probability of electron emission into vacuum in the emissive layer, thus improving the GaN ultraviolet The overall quantum efficiency of the photocathode can obtain higher ultraviolet sensitivity; 2) Since the forbidden band width of the Ga _x Al _1-x N multi-component mixed crystal emission layer material changes correspondingly with the change of x, the corresponding ultraviolet response threshold can be 3) The structure of this ultraviolet photocathode material can be used as a high-efficiency ultraviolet cold electron source, applied to microwave tubes, cyclotron accelerometers and other devices; it can also be used as a photosensitive element of active ultraviolet detectors, applied to ultraviolet alarms, etc. field.

The present invention will be described in further detail below in conjunction with the accompanying drawings.

Description of drawings

FIG. 1 is a schematic diagram of the layer structure of the GaN ultraviolet photocathode material of the present invention.

Fig. 2 is a working principle diagram of the GaN ultraviolet photocathode material of the present invention.

Detailed ways

1 and 2, a multi-component, gradient-doped GaN ultraviolet photocathode material structure of the present invention, the material structure is a substrate 1, an unintentionally doped AlN buffer layer 2, p Type _{GaxAl1 -xN} multi-component mixed crystal photoemission layer 3 and Cs or Cs/O active layer 4. The substrate 1 is double-sided polished sapphire. The unintentionally doped AlN buffer layer 2 is epitaxially grown on the substrate 1 with a thickness between 10-200nm. The p-type Ga _x Al _1-x N multi-component mixed crystal photoelectric emission layer 3 is epitaxially grown on the AlN buffer layer 2, the thickness is between 100-200 nm, and the doping concentration range is 10 ¹⁶ -10 ¹⁹ cm ^-3 , the doping concentration decreases sequentially from the body to the surface, and the ratio control parameter x in the Ga _x Al _1-x N multi-component mixed crystal gradually changes from 0 to 1 with the AlN buffer layer as the growth starting point. The Cs or Cs/O active layer 4 is adsorbed on the front surface of the p-type _{GaxAl1 -xN} multi-component mixed crystal photoelectric emission layer 3, and its thickness is on the order of nm.

A method for manufacturing a multi-component, gradient doped GaN ultraviolet photocathode material structure, comprising the following steps:

Step 1, on the upper surface of the double-sided polished sapphire substrate 1, grow an unintentionally doped AlN buffer layer 2 through the epitaxial growth process of semiconductor materials; the thickness of the unintentionally doped AlN buffer layer 2 is 10- 200nm.

Step 2, grow a p-type Ga _x Al _1-x N multi-component mixed crystal photoemission layer on the AlN buffer layer 2 obtained in step 1 by epitaxial growth process and p-type doping process of III-V compound semiconductor materials 3 as a photoemissive material; the p-type Ga _x Al _1-x N multi-component mixed crystal photoemissive layer 3 has a thickness of 100-200 nm, its doping concentration ranges from 10 ¹⁶ to 10 ¹⁹ cm ^-3 and is doped The concentration decreases sequentially from the body to the surface, and the ratio control parameter x in the _{GaxAl1 -xN} multi-component mixed crystal gradually changes from 0 to 1 with the AlN buffer layer as the growth starting point.

Step 3. Use chemical cleaning to remove the grease on the surface of the cathode material obtained in step 2 and the remaining inorganic attachments during processing; then send it into an ultra-high vacuum system to heat and purify the surface of the material to make the surface of the material reach atomic level cleanliness degree; when the material surface is heated and purified, the temperature is 700-900° C., and the heating time is 10-30 minutes.

Step 4. Adsorb a single layer of Cs or multiple layers of Cs/O on the surface of the p-type GaN material through an activation process to form a Cs or Cs/O activation layer 4, and finally prepare a multi-component, gradient Doped structure GaN ultraviolet photocathode.

2, the working principle of the reflective GaN ultraviolet photocathode material structure of the present invention is: the working mode of the ultraviolet photocathode material is reflective, that is, the ultraviolet light is incident from the front surface of the cathode, and is absorbed by the p-type GaN through the active layer 4. _x Al _1-x N multi-component mixed crystal photoemission layer 3 absorbs, and the photoemission layer 3 obtains energy after absorbing photons. When the incident photon energy is greater than the forbidden band width of GaN material (Eg=3.4eV), it is in the valence band The electrons can jump to the conduction band to become free electrons, and these free electrons reach the surface of the cathode through diffusion and drift and are emitted into the vacuum. The Ga _x Al _1-x N multi-component structure improves the escape probability of photoexcited electrons deep in the emissive layer on the one hand, and increases the adjustment of the ultraviolet response wavelength on the other hand. When the electrons are emitted into the vacuum, they are collected by an external strong voltage, and output in the form of photocurrent through an external collection circuit. The stronger the incident ultraviolet light is, the more photon energy is absorbed by the p-type _{GaxAl1 -xN} multi-component mixed crystal photoemission layer 3, and the output photocurrent is also larger.

Below in conjunction with embodiment the present invention is described in further detail:

Embodiment 1: as shown in Figure 1, a kind of reflective GaN ultraviolet photocathode material structure, this material structure is made up of substrate 1 (such as sapphire), unintentional doping AlN buffer layer 2, p-type Ga _x Al _1-x N multi-component mixed crystal photoelectric emission layer 3 and Cs or Cs/O active layer 4; wherein, the unintentionally doped AlN buffer layer 2 is epitaxially grown on the substrate layer 1 with a thickness of 50nm; p-type Ga _x Al _1-x N multi-component mixed crystal photoemissive layer 3 is epitaxially grown on the aforementioned AlN buffer layer 2 with a thickness of 120nm and doping concentrations of 1×10 ¹⁸ , 4×10 ¹⁷ , 2×10 ¹⁷ and 6×10 ¹⁶ , which gradually decreases from the body to the body surface, the proportion control parameter x in the mixed crystal starts from the AlN buffer layer, and gradually changes from 0 to 1; the Cs active layer 4 is adsorbed on the p-type Ga _x by the ultra-high vacuum activation process On the front surface of the Al _1-x N multicomponent mixed crystal photoelectric emission layer 3 , the thickness is one monoatomic layer.

Embodiment 2: Different from Embodiment 1, the thickness of the AlN buffer layer is 100nm; the p-type _{GaxAl1 -xN} multi-component mixed crystal photoemission layer 3 is epitaxially grown on the aforementioned AlN buffer layer 2, and the thickness is 120nm , the doping concentration is 1×10 ¹⁸ , 4×10 ¹⁷ , 2×10 ¹⁷ and 6×10 ¹⁶ , which gradually decrease from the body to the body surface. The proportion control parameter x in the mixed crystal takes the AlN buffer layer as the growth starting point, from 0 gradually becomes 1; the Cs active layer 4 is adsorbed on the front surface of the p-type Ga _x Al _1-x N multi-component mixed crystal photoemission layer 3 through an ultra-high vacuum activation process, with a thickness of one monoatomic layer.

Embodiment 3: Different from Embodiment 1, the thickness of the AlN buffer layer is 100nm; the p-type Ga _x Al _1-x N multi-component mixed crystal photoemission layer 3 is epitaxially grown on the aforementioned AlN buffer layer 2 with a thickness of 150nm , the doping concentration is 1×10 ¹⁸ , 4×10 ¹⁷ , 2×10 ¹⁷ and 6×10 ¹⁶ , which gradually decrease from the body to the body surface. The proportion control parameter x in the mixed crystal takes the AlN buffer layer as the growth starting point, from 0 gradually becomes 1; the Cs active layer 4 is adsorbed on the front surface of the p-type Ga _x Al _1-x N multi-component mixed crystal photoemission layer 3 through an ultra-high vacuum activation process, with a thickness of one monoatomic layer.

Embodiment 4: Different from Embodiment 1, the thickness of the AlN buffer layer is 10 nm; the p-type Ga _x Al _1-x N multi-component mixed crystal photoemission layer 3 is epitaxially grown on the aforementioned AlN buffer layer 2, and the thickness is 100 nm , the doping concentration is 1×10 ¹⁸ , 4×10 ¹⁷ , 2×10 ¹⁷ and 6×10 ¹⁶ , which gradually decrease from the body to the body surface. The proportion control parameter x in the mixed crystal takes the AlN buffer layer as the growth starting point, from 0 gradually becomes 1; the Cs active layer 4 is adsorbed on the front surface of the p-type Ga _x Al _1-x N multi-component mixed crystal photoemission layer 3 through an ultra-high vacuum activation process, with a thickness of one monoatomic layer.

Embodiment 5: Different from Embodiment 1, the thickness of the AlN buffer layer is 200nm; the p-type _{GaxAl1 -xN} multi-component mixed crystal photoemission layer 3 is epitaxially grown on the aforementioned AlN buffer layer 2, and the thickness is 200nm , the doping concentration is 1×10 ¹⁸ , 4×10 ¹⁷ , 2×10 ¹⁷ and 6×10 ¹⁶ , which gradually decrease from the body to the body surface. The proportion control parameter x in the mixed crystal takes the AlN buffer layer as the growth starting point, from 0 gradually becomes 1; the Cs active layer 4 is adsorbed on the front surface of the p-type Ga _x Al _1-x N multi-component mixed crystal photoemission layer 3 through an ultra-high vacuum activation process, with a thickness of one monoatomic layer.

The manufacturing method of the reflective GaN ultraviolet photocathode material structure is as follows:

First, on the upper surface of the double-sided polished sapphire substrate 1, grow by semiconductor material epitaxial growth process (such as metal organic chemical vapor deposition, Metalorganic Chemical Vapor Deposition, MOCVD and molecular beam epitaxy, Molecular Beam Epitaxy, MBE, etc.) An unintentionally doped AlN buffer layer 2 of the thickness; secondly, grow the AlN buffer layer 2 of the thickness, doped The p-type Ga _x Al _1-x N multi-component mixed crystal photoemission layer 3 with a dopant concentration range of 10 ¹⁶ -10 ¹⁹ cm ^-3 is used as the photoemission material; again, the cathode material obtained by epitaxial growth is chemically cleaned (such as Use 2:2:1 mixture of concentrated sulfuric acid, H ₂ O ₂ and deionized water to clean the surface of the material) to remove the grease on the surface of the emission layer and the remaining inorganic attachments during processing; then send it to the ultra-high vacuum system For example, heat and purify the surface of the material at 710°C for 30 minutes to make the surface of the material reach atomic level cleanliness; finally, pass through the surface of the obtained p-type Ga _x Al _1-x N multi-component mixed crystal material The activation process adsorbs single-layer Cs or multi-layer Cs/O to form a Cs or Cs/O active layer, and finally prepares a GaN ultraviolet photocathode with negative electron affinity.

The present invention is not limited to the restrictions on the buffer layer, photoemission layer thickness and activation layer thickness, as long as the simple changes made in the structure of the technical solution of the present invention, all fall into the protection scope of the present invention.

Claims (9)

1. a multicomponent, grade doping GaN ultraviolet light photo-cathode material structure is characterized in that this material structure is followed successively by AlN resilient coating (2), the p type Ga of substrate (1), involuntary doping from bottom to top _xAl _1-xN multicomponent mixed crystal photoemissive layer (3) and Cs or Cs/O active coating (4).

2. multicomponent according to claim 1, grade doping GaN ultraviolet light photo-cathode material structure is characterized in that described substrate (1) is the sapphire of twin polishing.

3. multicomponent according to claim 1, grade doping GaN ultraviolet light photo-cathode material structure is characterized in that, AlN resilient coating (2) epitaxial growth of described involuntary doping is on substrate (1), and thickness is between 10-200nm.

4. multicomponent according to claim 1, grade doping GaN ultraviolet light photo-cathode material structure is characterized in that, described p type Ga _xAl _1-xN multicomponent mixed crystal photoemissive layer (3) epitaxial growth is on AlN resilient coating (2), and thickness is between 100-200nm, and the doping content scope is 10 ¹⁶-10 ¹⁹Cm ^-3, doping content is from reducing Ga successively to the surface in the body _xAl _1-xThe proportional control parameter x serves as the growth starting point with the AlN resilient coating in the N multicomponent mixed crystal, fades to 1 from 0.

5. multicomponent according to claim 1, grade doping GaN ultraviolet light photo-cathode material structure is characterized in that, described Cs or Cs/O active coating (4) are adsorbed on p type Ga _xAl _1-xOn the front surface of N multicomponent mixed crystal photoemissive layer (3), thickness is at the nm order of magnitude.

6. a method of making the described multicomponent of claim 1, grade doping GaN ultraviolet light photo-cathode material structure is characterized in that, may further comprise the steps:

Step 1, at the upper surface of the Sapphire Substrate (1) of twin polishing, by the grow AlN resilient coating (2) of involuntary doping of the epitaxial growth technology of semi-conducting material;

Step 2, by the p type doping process of epitaxial growth technology and III-V group iii v compound semiconductor material, go up growing p-type Ga at the AlN resilient coating (2) that step 1 obtains _xAl _1-xN multicomponent mixed crystal photoemissive layer (3) is as photoemissive material;

Remaining inorganic attachment in step 3, the surperficial grease of the cathode material that utilizes chemical cleaning removal step 2 to obtain and the course of processing; Then it is sent in the ultra-high vacuum system, material surface is added thermal purification, make material surface reach the atom level clean level;

Step 4, at above-mentioned p type GaN material surface by activation technology absorption monolayer Cs or multi-layer C s/O, to form Cs or Cs/O active coating (4), finally prepare multicomponent, grade doping structure GaN ultraviolet light photo negative electrode with negative electron affinity.

7. according to the method for the described manufacturing multicomponent of claim 6, grade doping GaN ultraviolet light photo-cathode material structure, it is characterized in that the thickness of the AlN resilient coating (2) of involuntary doping in the step 1 is 10-200nm.

8. according to the method for the described manufacturing multicomponent of claim 6, grade doping GaN ultraviolet light photo-cathode material structure, it is characterized in that p type Ga in the step 2 _xAl _1-xThe thickness of N multicomponent mixed crystal photoemissive layer (3) is 100-200nm, and its doping content scope is 10 ¹⁶-10 ¹⁹m ^-3And doping content is from reducing described Ga successively to the surface in the body _xAl _1-xThe proportional control parameter x serves as the growth starting point with the AlN resilient coating in the N multicomponent mixed crystal, fades to 1 from 0.

9. according to the method for the described manufacturing multicomponent of claim 6, grade doping GaN ultraviolet light photo-cathode material structure, it is characterized in that the temperature when in the step 3 material surface being added thermal purification is 700-900 ℃, be 10-30 minute heating time.

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