CN101447378A

CN101447378A - Reflection type GaN ultraviolet light photo-cathode material structure and manufacture method thereof

Info

Publication number: CN101447378A
Application number: CNA2008102333225A
Authority: CN
Inventors: 杜晓晴; 常本康; 钱芸生; 赵红; 王晓兰
Original assignee: Chongqing University
Current assignee: Chongqing University
Priority date: 2008-12-11
Filing date: 2008-12-11
Publication date: 2009-06-03
Anticipated expiration: 2028-12-11
Also published as: CN100595858C

Abstract

The present invention provides a reflective GaN ultraviolet photocathode material structure and its manufacturing method. Its thickness direction consists of a substrate, an unintentionally doped GaN buffer layer, a p-type GaN photoemissive layer, and Cs or Cs/O The composition of the active layer; wherein, the unintentionally doped GaN buffer layer is grown on the substrate; the p-type GaN photo-emitting layer is epitaxially grown on the GaN buffer layer; the Cs or Cs/O active layer is adsorbed on the p-type GaN photo-emitting layer On the front surface of the layer, the thickness is on the order of nm. The structure uses unintentionally doped GaN material as a buffer layer between the substrate material and the p-type GaN photoemissive material, thereby obtaining a GaN photoemissive material with zero interfacial recombination rate; improving the probability of electron emission to vacuum at the interface , and ultimately improve the overall quantum efficiency of the GaN UV photocathode; since the long-wavelength UV light will be absorbed at the interface between the GaN photoemissive layer and the buffer layer, this material structure with zero interfacial recombination rate can obtain higher long-wave UV sensitivity.

Description

A kind of reflection type GaN ultraviolet light photo-cathode material structure and preparation method thereof

Technical field

The invention belongs to the ultraviolet detection material technical field, be specifically related to the ultraviolet light photo-cathode material structure that a kind of based semiconductor material epitaxy technology, semi-conducting material doping techniques and ultra high vacuum surface activation technology combine.

Background technology

In recent years, along with improving and the development of ultra high vacuum technique of GaN material preparation technology, p type doping techniques, GaN ultraviolet light photo negative electrode is just becoming a kind of ultraviolet light photo negative electrode of novel high-performance.The surface of this negative electrode has negative electron affinity (NEA), be that the surface vacuum energy level of negative electrode is lower than in the body energy level at the bottom of the conduction band, therefore light induced electron only need run to the surface in the body, just can be transmitted into vacuum easily and need not the potential barrier that superfluous kinetic energy removes to overcome material surface, the escape probability of electronics increases greatly like this, and be cold electron emission, therefore has the quantum efficiency height, dark emission is little, distinct advantages such as the emitted electron energy distribution is concentrated, its quantum efficiency is generally 30%, the quantum efficiency that is much higher than traditional cesium telluride ultraviolet light photo negative electrode 10% with positron affinity (PEA), and, GaN material energy gap is at～3.6eV, the following ultra-violet radiation of response 400nm is typical " day is blind " material, has good capability of resistance to radiation.

GaN ultraviolet light photo negative electrode can be worked under reflective or transmission-type.When light from the incident of negative electrode front surface and electronics is reflective work during surface emitting in the past also; When light from the rear surface incident of negative electrode and electronics is transmission-type work during surface emitting in the past.Reflective GaN ultraviolet light photo-cathode material structure generally comprises backing material (normally sapphire), epitaxial growth p type GaN photoemissive material and the low work function active coating on substrate from bottom to top.Wherein between backing material and the p type GaN material because material lattice constant difference big (about 16%), lattice does not match, therefore can cause these two kinds of material interfaces to produce bigger interface recombination rate, can in the photoelectron emissions process, capture the free electron that is excited, thereby reduce electronics emission quantity, finally cause a lower cathode quantum efficiency.

Find that by literature search the reflection type GaN ultraviolet light photo negative electrode of external preparation generally adopts the AlN resilient coating to overcome the problems referred to above that lattice does not match and causes between backing material and p type GaN material.The lattice constant difference of AlN material and GaN material is about 3%, so the two can better mate.This structure is compared with the GaN material structure of direct extension on substrate, the photoelectric emission performance improves, but owing to still have certain crystal lattice difference between padded coaming AlN and the photoemissive material GaN, therefore still there is certain interface recombination rate in the interface between these two kinds of materials, influences the emission of electronics.

Summary of the invention

Have above-mentioned deficiency at prior art, the interface recombination rate that the purpose of this invention is to provide a kind of GaN photoemissive material is zero reflection type GaN ultraviolet light photo-cathode material new structure.

The object of the present invention is achieved like this: a kind of reflection type GaN ultraviolet light photo-cathode material structure is characterized in that this material structure is made of GaN resilient coating, p type GaN photoemissive layer and Cs or the Cs/O active coating of substrate, involuntary doping at thickness direction from bottom to top; Wherein, the GaN buffer growth of involuntary doping is on substrate, and thickness is between 10-200nm; P type GaN photoelectric emission layer epitaxially grown is on described GaN resilient coating, and thickness is between 100-200nm, and doping content is 10 ¹⁷-10 ¹⁹Cm ^-3Between; Cs or Cs/O active coating are adsorbed on the front surface of p type GaN photoemissive layer, and thickness is at the nm order of magnitude.

The manufacture method of described reflection type GaN ultraviolet light photo-cathode material structure comprises the steps:

Step 1: the upper surface that has polished in Sapphire Substrate, the GaN resilient coating of the involuntary doping of the epitaxial growth technology growth 10-200nm thickness by semi-conducting material;

Step 2: then,, on the GaN resilient coating that step 1 obtains, grow 100-200nm thickness, doping content 10 by the p type doping process of epitaxial growth technology and GaN material ¹⁷-10 ¹⁹Cm ^-3P type GaN photoemissive layer as photoemissive material, the epitaxial material of the growth that obtains;

Step 3: the epitaxial material of the growth that step 2 is obtained is removed grease through chemical cleaning; Again it is sent in the ultra-high vacuum system, under 700-900 ℃, material surface carried out 10-30 minutes the thermal purification that adds, make material surface reach the atom level clean level;

Step 4: the p type GaN material surface absorption monolayer Cs or the multi-layer C s/O that step 3 are obtained by activation technology form Cs or Cs/O active coating, finally prepare the GaN ultraviolet light photo negative electrode with negative electron affinity.

Compared to existing technology, the present invention has following beneficial effect:

(1) the present invention proposes the reflective ultraviolet light photo-cathode material structure that a kind of based semiconductor material epitaxy technology, semi-conducting material doping techniques and ultra high vacuum surface activation technology combine, this structure adopts the GaN material of involuntary doping as the resilient coating between backing material and the p type GaN photoemissive material, thereby obtains to have the GaN photoemissive material of zero interface recombination rate; Improved at the interface that electronics is transmitted into the probability of vacuum, and finally improved the overall quantum efficiency of GaN ultraviolet light photo negative electrode.

(2) since long wavelength's ultraviolet light will be between GaN photoemissive layer and resilient coating absorption at the interface, therefore the material structure of this zero interface recombination rate can obtain higher long wave ultraviolet sensitivity.

(3) this ultraviolet light photo-cathode material structure can be used as a kind of cold electron source of ultraviolet efficiently, is applied to devices such as microwave tube, circular accelerator meter; Also can be used as the light-sensitive element of active ultraviolet detector, be applied to fields such as ultraviolet alarm.

Description of drawings

Fig. 1 is the layer structural representation of GaN ultraviolet light photo-cathode material of the present invention;

Fig. 2 is the fundamental diagram of the GaN ultraviolet light photo-cathode material of invention.

Embodiment

Below in conjunction with the drawings and specific embodiments the present invention is described in further detail.

Embodiment 1: as shown in Figure 1, a kind of reflection type GaN ultraviolet light photo-cathode material structure, this material structure are made of GaN resilient coating 2, p type GaN photoemissive layer 3 and Cs or the Cs/O active coating 4 of substrate 1 (as sapphire), involuntary doping from bottom to top; Wherein, the GaN resilient coating 2 of involuntary doping is grown on the substrate 1 by the semiconductor epitaxial growing technology, and thickness is 50nm; 3 epitaxial growths of p type GaN photoemissive layer are on described GaN resilient coating 2, and thickness is 100nm, and doping content is 5 * 10 ¹⁷On the front surface of p type GaN photoemissive layer 3, thickness is a monoatomic layer to Cs active coating 4 by ultra high vacuum activation technology adsorbed close.

Embodiment 2: with implement 1 different be that the thickness of GaN resilient coating 2 is 100nm; 3 epitaxial growths of p type GaN photoemissive layer are on described GaN resilient coating 2, and thickness is 100nm, and doping content is 5 * 10 ¹⁷On the front surface of p type GaN photoemissive layer 3, thickness is a monoatomic layer to Cs active coating 4 by ultra high vacuum activation technology adsorbed close.

Embodiment 3: with implement 1 different be that the thickness of GaN resilient coating 2 is 100nm; 3 epitaxial growths of p type GaN photoemissive layer are on described GaN resilient coating 2, and thickness is 150nm, and doping content is 5 * 10 ¹⁷On the front surface of p type GaN photoemissive layer 3, thickness is a monoatomic layer to Cs active coating 4 by ultra high vacuum activation technology adsorbed close.

The manufacture method of above-mentioned reflection type GaN ultraviolet light photo-cathode material structure is: at first, the upper surface that has polished in Sapphire Substrate 1, the GaN resilient coating 2 of the involuntary doping by thickness as described in epitaxial growth technology (as metal oxide chemical vapor deposition MOCVD, the molecular beam epitaxy MBE etc.) growth of semi-conducting material; Secondly, at the p type doping process by identical epitaxial growth technology and GaN material, the described thickness of growth, doping content are 10 on GaN resilient coating 2 ¹⁷-10 ¹⁸Cm ^-3P type GaN photoemissive layer 3 as photoemissive material; Then, the epitaxial material of the growth that obtains is removed grease through chemical cleaning (as utilizing the hydrofluoric acid clean material surface of purity 50%); Again it is sent in the ultra-high vacuum system and heat,, make material surface reach the atom level clean level as under 900 ℃, material surface being carried out 20 minutes the thermal purification that adds; At last, make p type GaN material surface absorption monolayer Cs or multi-layer C s/O, finally prepare GaN ultraviolet light photo negative electrode with negative electron affinity by activation technology.

The operation principle of reflection type GaN ultraviolet light photo-cathode material structure of the present invention is: this ultraviolet light photo-cathode material is reflective work, be that ultraviolet light goes into to shine from the front surface of negative electrode, absorbed by p type GaN photoemissive layer through active coating 4, the light of shorter wavelength absorbs on GaN photoemissive layer 3 surfaces, the light of longer wavelength absorbs in GaN photoemissive layer 3 bodies, and more long wavelength's light will be in the absorption at the interface between GaN photoemissive layer 3 and the resilient coating 2; After absorbing photon, GaN photoemissive layer 3 obtains energy, when incident photon energy during greater than the energy gap (3.4eV) of GaN material, the electronics that is in valence band just can transit to conduction band becomes free electron, and these free electrons arrive cathode surface and are transmitted into vacuum by diffusion.For the free electron that produces at the interface, because the GaN material that adopts involuntary doping among the present invention is as resilient coating 2, it and p type GaN photoemissive layer 3 are same materials, so do not have the interface recombination rate, thereby have avoided electronics compound at the interface.After electronics is transmitted into vacuum, collected, and export with the photoelectric current form by adding Acquisition Circuit by plus high-pressure.The ultraviolet light of incident is strong more, and the photon energy that GaN absorbs is just many more, and the photoelectric current of output is big more.

The present invention is not limited to the restriction of described enforcement to the thickness of resilient coating, photoelectric emission layer thickness and active coating, as long as the simple change of being done on the structure of technical solution of the present invention all falls into protection scope of the present invention.

Claims

1. A reflective GaN ultraviolet photocathode material structure, characterized in that the material structure consists of a substrate (1), an unintentionally doped GaN buffer layer (2), a p-type GaN photoelectric cathode from bottom to top in the thickness direction The emission layer (3) and the Cs or Cs/O activation layer (4) are composed.

2. The reflective GaN ultraviolet photocathode material structure according to claim 1, characterized in that the unintentionally doped GaN buffer layer (2) is grown on the substrate (1) with a thickness between 10-200nm between.

3. The reflective GaN ultraviolet photocathode material structure according to claim 1, characterized in that the p-type GaN photoemissive layer (3) is epitaxially grown on the GaN buffer layer (2), with a thickness of 100- 200nm, the doping concentration is between 10 ¹⁷ —10 ¹⁹ cm ^-3 .

4. The reflective GaN ultraviolet photocathode material structure according to claim 1, characterized in that the Cs or Cs/O active layer (4) is adsorbed on the front surface of the p-type GaN photoemissive layer (3), The thickness is on the order of nm.

5. The method for making the reflective GaN ultraviolet photocathode material structure according to claim 1, comprising the steps of:

Step 1: On the polished upper surface of the sapphire substrate (1), grow an unintentionally doped GaN buffer layer (2) with a thickness of 10-200 nm through the epitaxial growth process of semiconductor materials;

Step 2: Then, through the epitaxial growth process and the p-type doping process of GaN material, grow a 100-200nm thick GaN buffer layer (2) with a doping concentration of 10 ¹⁷ -10 ¹⁹ cm ^-3 on the GaN buffer layer (2) obtained in step 1 The p-type GaN photoemission layer (3) is used as a photoemission material, and the obtained epitaxial material is grown;

Step 3: The grown epitaxial material obtained in Step 2 is chemically cleaned to remove grease; then it is sent to an ultra-high vacuum system, and the surface of the material is heated and purified at 700-900°C for 10-30 minutes to make the material The surface is atomically clean;

Step 4: Adsorb a single layer of Cs or multiple layers of Cs/O on the surface of the p-type GaN material obtained in step 3 through the activation process to form a Cs or Cs/O activation layer (4), and finally prepare a GaN ultraviolet photocathode.