CN103972310B - A kind of preparation method of zinc oxide based p type material - Google Patents

Abstract

The invention provides a method for preparing a zinc oxide-based p-type material, which belongs to the technical field of semiconductor material growth. The method prepares a gradient layer on the base layer; prepares a cover layer on the gradient layer; the base layer is a Mg _x Zn _1-x O (0.6≥x≥0.2) material on the oxygen polar surface, and the thickness of the base layer is not Less than 5nm; the gradient layer has a composition gradient structure, and its structure from bottom to top is Mg _x Zn _1-x O/Mg _x-δ Zn _1-(x-δ) O/Mg _x-2δ Zn _{1-(x -2δ)} O/.../Mg _x-(n-1)δ Zn _{1-[x-(n-1)δ]} O/Mg _x-nδ Zn _1-(x-nδ) O(δ→0,n is a natural number; nδ=x;), the thickness of the gradient layer is not greater than 1 μm; the material of the cover layer is ZnO, and the thickness of the cover layer is not less than 300nm. The zinc oxide-based p-type material prepared by the method has good temperature stability.

Description

A kind of preparation method of zinc oxide-based p-type material

technical field

The invention belongs to the technical field of semiconductor material growth, and in particular relates to a preparation method of a zinc oxide-based p-type material.

Background technique

Wide bandgap semiconductors are called third-generation semiconductors because of their broad application prospects in solid-state lighting, short-wavelength semiconductor lasers, and ultraviolet light detection. ZnO is one of the representatives of wide bandgap semiconductor materials. It is a uniaxially symmetric direct bandgap semiconductor. The warm ionization energy (26meV) can ensure efficient exciton luminescence and low-threshold stimulated emission at room temperature. Therefore, ZnO is considered to be an ideal material for short-wavelength light-emitting diodes (LEDs), especially lasers (LDs) and other optoelectronic devices. Compared with other wide bandgap semiconductor materials, ZnO also has abundant resources and low cost of raw materials; it is environmentally friendly, non-toxic and harmless; the method of film formation is simple and diverse, and the growth temperature is low; it is easy to obtain semiconductor materials that can be used as substrates to achieve homogeneity Epitaxy; compatible with wet etching process, conducive to optoelectronic integration and other advantages. Based on the above reasons, research on ZnO-based semiconductor optoelectronic materials has become an international frontier and hot spot. Considering that ZnO-based materials may meet the country's strategic needs for key components such as short-wavelength semiconductor lasers and ultraviolet photodetectors on a series of major issues related to national defense security and national economic development such as space interstellar communications.

At present, the research on ZnO at home and abroad has achieved a series of gratifying research results. After Japanese scientists obtained the electroluminescence of ZnO homojunction on a low-mismatch scandium aluminum magnesium oxide substrate in 2004, in 2005, the research group of wide-bandgap II-VI semiconductors of the State Key Laboratory of Luminescence and Applications in For the first time in the world, a ZnO homogeneous pn junction LED based on a sapphire substrate was prepared, and blue-violet electroluminescence at room temperature was obtained. Subsequently, many research groups at home and abroad have also reported ZnO homogeneous pn junctions and LEDs based on quantum well structures. Electroluminescence. It is worth mentioning that Ryu et al. used BeZnO as the barrier layer and ZnO as the well layer to prepare quantum well-type ZnO-based LEDs and LDs, and obtained ultraviolet electroluminescence and laser emission. The blue-violet band laser emission belonging to ZnO has also been obtained in the heterostructure, and its threshold current is only 0.8mA, which shows that ZnO-based materials are fully capable of meeting the needs of short-wave optoelectronic devices such as ultraviolet luminescence and low-threshold ultraviolet laser devices.

However, due to the high ionization energy of acceptor impurities in ZnO, the performance of p-type ZnO-based materials prepared by traditional methods cannot meet the device requirements. The lack of methods and processes for preparing p-type ZnO materials with high repeatability, stability, low resistance, and high mobility is still the bottleneck that prevents ZnO-based optoelectronic devices from going out of the laboratory.

The traditional preparation of p-type ZnO materials mainly relies on the doping of group I and group V elements into the material through different technical means, respectively or simultaneously, in order to realize the acceptor state of the above two groups of elements in ZnO. However, theoretical and experimental results show that the acceptor activation energy of acceptor impurities that can be applied to ZnO materials is mostly above 200meV, and we can easily obtain the relationship between the ionization rate of acceptor impurities and the acceptor activation energy. The acceptor ionization rate is less than 1/1000, so it cannot effectively provide holes at all. Therefore, people have to use low-temperature growth and heavy doping to ensure that there are enough acceptors in the material to increase the concentration of holes. However, both lower growth temperature and excessive doping of impurities will cause the deterioration of the crystal quality of the material. , aggravate the hindering effect of dislocation scattering, neutral impurity scattering and ionized impurity scattering on hole transport, directly affect the hole mobility and other physical properties of the material, and seriously interfere with the stability of material performance. Some people also expect to reduce the acceptor energy level through energy band modulation engineering, so that acceptor impurities can be easily ionized, but no effective technical means have been obtained yet. It can be seen that the high activation energy of the acceptor is the main difficulty in preparing p-type ZnO-based materials. If there is a method or process that can make p-type ZnO doping get rid of the constraints of high acceptor activation energy, so that the generation of holes no longer depends on the "spontaneous ionization" of the acceptor, it can be obtained at a relatively low impurity doping concentration. Obtain higher hole concentration, improve the effectiveness of acceptor impurities, reduce the hindrance of defects to holes, and realize efficient, stable and repeatable p-ZnO.

Contents of the invention

The object of the present invention is to provide a method for preparing a zinc oxide-based p-type material in order to solve the problems of poor stability and low repeatability of the existing zinc oxide-based p-type material preparation method.

The invention provides a method for preparing a zinc oxide-based p-type material, the method comprising:

Prepare a gradient layer on top of the base layer;

preparing a cover layer on the gradient layer;

The base layer is a Mg _x Zn _1-x O (0.6≥x≥0.2) material with an oxygen polar surface, and the thickness of the base layer is not less than 5nm;

The graded layer has a composition graded structure, and its structure is expressed as Mg _x Zn _1-x O/Mg _x-δ Zn _1-(x-δ) O/Mg _x-2δ Zn _{1-( x-2δ)} O/.../Mg _x-(n-1)δ Zn _{1-[x-(n-1)δ]} O/Mg _x-nδ Zn _1-(x-nδ) O(δ→0, n is a natural number; nδ=x; abbreviated as graded-MgZnO), the thickness of the graded layer is not greater than 1 μm;

The material of the cover layer is ZnO, and the thickness of the cover layer is not less than 300nm.

Preferably, the thickness of the base layer is 20-50nm.

Preferably, the gradient layer has a thickness of 50nm-200nm.

Preferably, the thickness of the cover layer is 1 μm-3 μm.

Preferably, the base layer is prepared on a substrate.

Principle of the invention

The invention provides a method for preparing a zinc oxide-based p-type material. The method is to grow a graded-MgZnO material layer with a gradually changing composition on the Mg _x Zn _1-x O material on the oxygen polar surface, so that the material is generated inside the material. The directions of piezoelectric polarization and spontaneous polarization are consistent, and under the combined action of the two polarizations, the adjacent Mg _y-δ Zn _1-(y-δ) O/Mg _y Zn _1-y O (y is Any value between δ to nδ, δ→0) Charge accumulation will occur on the high magnesium component side, and the amount of charge accumulation increases with the increase of the thickness of the graded-MgZnO material layer, and the electric field formed due to charge accumulation will make The energy band is tilted, in order to neutralize the charge generated by the polarization and the small energy band tilt, so that the system is in an equilibrium state, the acceptor will be forced to ionize and generate holes, and these holes will eventually be on the side of the graded-MgZnO material layer Enrich and form a three-dimensional hole layer, and work as carriers. The method of the present invention can achieve hole injection only through the field-induced hole injection generated by the heterostructure without the doping of acceptor impurities; and for materials doped with acceptor impurities, as long as the polarization charge accumulation Sufficient, most acceptors will ionize, and this ionization will not be limited by the ionization energy, also because it is not affected by the main ionization energy, the p-ZnO-based material obtained by the polarization induction method has a hole The concentration is not greatly affected by temperature, which makes it have good temperature stability.

Beneficial effects of the present invention

The invention provides a method for preparing a zinc oxide-based p-type material. The method applies a polarization induction method to a ZnO-based wide bandgap material system to prepare a p-type ZnO-based material. The polarization induction method utilizes polarization accumulation The charge and electric field promote the ionization of acceptors, and its application makes ZnO-based materials get rid of the limitation of high ionization energy of acceptors. Compared with the traditional method of "spontaneous ionization" of "sit and wait" acceptors, it can be called "active attack". ; By means of polarization induction, the ionization rate of the acceptor and the doping efficiency of the acceptor impurity can be greatly improved, and the difficult problem of p-type doping of ZnO-based materials can be solved. Affected by the main ionization energy, the electrical properties of the material prepared by this method are not greatly affected by temperature, and have good temperature stability.

Description of drawings

Fig. 1 is a schematic structural view of the zinc oxide-based p-type material obtained by the preparation method of the present invention.

Fig. 2 is a graph showing the relationship between the Mg and Zn components in the graded layer of the ZnO-based p-type material prepared by the method of the present invention and the thickness of the graded layer.

detailed description

The present invention provides a kind of preparation method of zinc oxide-based p-type material, as shown in Figure 1, the method comprises:

Prepare a gradient layer 103 on the base layer 102;

Prepare a cover layer 104 on the gradient layer 103;

The base layer 102 is a Mg _x Zn _1-x O material with an oxygen polar surface, and the thickness of the base layer is not less than 5 nm, preferably 20-50 nm. polarity control;

The gradient layer 103 has a composition gradient structure, and the Mg composition of the gradient layer gradually decreases from x (0.6≥x≥0.2) in the base layer to 0 as the thickness changes, and its structure can be expressed as Mg _x Zn from bottom to top _1-x O/Mg _x-δ Zn _1-(x-δ) O/Mg _x-2δ Zn _1-(x-2δ) O/…/Mg _x-(n-1)δ Zn _{1-[x- (n-1)δ]} O/Mg _x-nδ Zn _1-(x-nδ) O(ZnO) (δ→0, n is a natural number; nδ=x; abbreviated as graded-MgZnO), δ is 0-1 A certain value close to 0 in order to ensure that the Mg composition changes continuously from x with a certain gradient value, which can be considered as the gradient of the Mg composition. The Mg composition on the lower surface of the gradient layer is consistent with the base layer, that is, Mg _x Zn _1-x O (0.6≥x≥0.2), the Mg content on the upper surface of the gradient layer is 0, that is, ZnO, and the thickness of the gradient layer is not greater than 1 μm (micrometer), preferably 50nm to 200nm;

The material of the cover layer 104 is ZnO, and the thickness of the cover layer is not less than 300nm, preferably in the range of 1 μm to 3 μm. The electric polarization is in the same direction as the spontaneous polarization of the material.

The base layer 102 of the present invention can exist independently, and is preferably prepared on the substrate 101 .

The base layer 102, gradient layer 103 and cover layer 104 of the present invention are all oxygen polar.

The preparation of the material of the graded layer of the present invention is prior art, the graded layer of the present invention is not unique, also can be the alloy of other metals except Mg and ZnO, as Be _x Zn _1-x O/Be _x-δ Zn _1-(x-δ) O/Be _x-2δ Zn _1-(x-2δ) O/…/Be _x-(n-1)δ Zn _{1-[x-(n-1)δ ]} O/Be _x-nδ Zn _1-(x-nδ) O(ZnO) (δ→0, n is a natural number; nδ=x), but the selected base layer and cover layer should match the gradient layer, so that the whole structure The spontaneous polarization in is in the same direction as the piezoelectric polarization. The base layer of the present invention can be doped with known ZnO acceptor impurities. For example, the acceptor impurities can be group V elements such as N, P, As, Sb, or group I elements such as Li, Na, and K.

Fig. 2 is the relationship curve of the change of Mg and Zn composition with the thickness in the graded layer in the ZnO-based p-type material prepared by the inventive method, in the figure, the horizontal axis represents the composition, and the vertical axis represents the thickness counted from the substrate surface, X refers to the composition of Mg in the upper surface of the gradient layer. Curve 201 shows the change of Mg composition with thickness, and curve 202 shows the change of Zn composition with thickness. Curve 201 and curve 202 are the structures on the right There is a corresponding relationship. From the curve 201, we can see that the Mg composition gradually decreases from X to 0 with the thickness of the gradient layer, and correspondingly, the Zn composition shown in the curve 202 gradually increases from (1-X) to 1. Note that this trend is linear. In this way, the base layer can realize lattice restraint to the lower surface of the graded layer, and in the graded layer, adjacent Mg _y-δ Zn _1-(y-δ) O/Mg _y Zn _1-y O (y is any One value, δ→0) The spontaneous polarization and piezoelectric polarization between the layers are superimposed in the same direction, and the capping layer binds the upper surface of the gradient layer.

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

Example 1

The specific implementation method of preparing polarization-induced p-type ZnO material by MOCVD

Zinc source adopts diethyl zinc, magnesium source adopts dimethyl dimagnesocene, oxygen source adopts oxygen, zinc source and magnesium source are contained in bubble bottles, and the active ingredients in the bubble bottles are carried by carrier gas (nitrogen) It can be seen that the organic source pipeline of the MOCVD system in this embodiment is a standard pipeline, so the amount of the source passed into the reaction chamber is related to the temperature of the source and the flow rate of the carrier gas (the higher the temperature of the source, the greater the flow rate of the carrier gas, the greater the flow rate of the carrier gas through the greater the amount of source that enters the reaction chamber).

Step 1, substrate preparation: clean the C-plane sapphire substrate with oxygen polarity, and place it in the MOCVD reaction chamber (corresponding to 101 shown in Figure 1)

Step 2, growing the Mg _x Zn _1-x O base layer on the surface of the sapphire substrate: zinc source temperature is 0°C, carrier gas flow rate is 10 sccm, oxygen flow rate is 60 sccm; magnesium source is 70°C, carrier gas flow rate is 20 sccm. A 30nm base layer is grown on the surface of the graded layer. The Mg component in Mg _x Zn _1-x O is 30%, that is, Mg _0.3 Zn _0.7 O, which is oxygen polarity (corresponding to 102 shown in Figure 1)

Step 3, grow the gradient layer on the base layer: keep the temperature of the zinc source at 0°C, the flow rate of the carrier gas at 10 sccm, and the flow rate of oxygen at 60 sccm, and continue to pass into the reaction chamber; at the same time, the magnesium source is passed into the reaction chamber, and the temperature of the magnesium source is from The temperature was lowered from 70°C to 20°C at a rate of 0.05°C/5s, and the carrier gas flow rate was 20sccm. Due to the decrease of source temperature, the content of magnesium source in the reaction chamber gradually decreased, so that the content of magnesium in the prepared film gradually decreased. A 70nm graded layer is grown on the base layer. (corresponding to 103 shown in Figure 1)

Step 4, growing the ZnO capping layer on the graded layer: keep the temperature of the zinc source at 0° C., the flow rate of the carrier gas at 10 sccm, the flow rate of oxygen at 60 sccm, and stop feeding the magnesium source. A 1 μm thick Zn polar surface ZnO base layer (corresponding to 104 shown in FIG. 1 ) is deposited on the graded layer.

The descriptions of the above embodiments are only used to help understand the method and core idea of the present invention. It should be pointed out that for those skilled in the art, without departing from the principles of the present invention, some improvements and modifications can be made to the present invention, and these improvements and modifications also fall within the protection scope of the claims of the present invention.

The above description of the disclosed embodiments is provided to enable any person skilled in the art to make or use the invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the invention. Therefore, the present invention will not be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims (5)

1. A preparation method for zinc oxide-based p-type material, characterized in that the method comprises: Prepare a gradient layer on top of the base layer; preparing a cover layer on the gradient layer; The base layer is a Mg _x Zn _1-x O material with an oxygen polar surface, where 0.6≥x≥0.2, and the thickness of the base layer is not less than 5 nm; The graded layer has a composition graded structure, and its structure is expressed as Mg _x Zn _1-x O/Mg _x-δ Zn _1-(x-δ) O/Mg _x-2δ Zn _{1-( x-2δ)} O/.../Mg _x-(n-1)δ Zn _{1-[x-(n-1)δ]} O/Mg _x-nδ Zn _1-(x-nδ) O where δ→0 , n is a natural number, nδ=x, and the thickness of the gradient layer is not greater than 1 μm; The material of the cover layer is ZnO, and the thickness of the cover layer is not less than 300nm. 2 . The method for preparing a zinc oxide-based p-type material according to claim 1 , wherein the thickness of the base layer is 20-50 nm. 3 . The method for preparing a zinc oxide-based p-type material according to claim 1 , wherein the thickness of the graded layer is 50 nm to 200 nm. 4 . 4 . The method for preparing a zinc oxide-based p-type material according to claim 1 , wherein the thickness of the capping layer is 1 μm˜3 μm. 5. The method for preparing a zinc oxide-based p-type material according to claim 1, wherein the base layer is prepared on a substrate.