CN103060757B - Method for Li-doped growth of p-type transparent conductive Ni1-xMgxO crystal film - Google Patents

Abstract

A method for Li-doped growth of p-type transparent conductive Ni _1-x Mg _x O crystal thin film is to use pulsed laser deposition method, mix NiO, MgO and Li ₂ CO ₃ powders by ball milling, pressing and sintering at high temperature to obtain Li-doped Ni _1-x Mg _x O ceramic target; then put the ceramic target and substrate into the pulsed laser deposition device, adjust the distance between the target and the substrate, under the appropriate substrate temperature, oxygen pressure and laser frequency grow, and then cool to room temperature to obtain a Li-doped Ni _1-x Mg _x O crystal thin film. The crystal thin film prepared by the method of the present invention has p-type conductance, has excellent characteristics such as low resistivity, high transmittance, high carrier mobility, and continuously adjustable band gap; and the method is simple, and real-time doping is realized. The concentration is controlled by adjusting the growth temperature and the content of Li and Mg in the target, and the obtained film has broad application prospects in the fields of transparent electronics and optoelectronic devices.

Description

Method for Li-doped growth of p-type transparent conductive Ni1-xMgxO crystal film

technical field

The invention relates to a method for growing a p-type transparent conductive Ni _1-x Mg _x O crystal thin film doped with Li, and belongs to the technical field of p-type transparent conductive thin films.

Background technique

Transparent conductive oxide (TCO) thin film is an important optoelectronic material, because of its unique combination of transparency and conductivity, it has broad application prospects in solar cells, flat-panel liquid crystal displays, light-emitting diodes and other fields. n-type TCO materials, such as ITO (In ₂ O ₃ :Sn), FTO (SnO ₂ :F) and AZO (ZnO:Al), have achieved relatively good photoelectric properties and have been widely used in commercial products.

However, there are few types of corresponding p-type TCO materials, and their photoelectric properties are far from those of n-type TCOs, which limits their applications in transparent electronic and optoelectronic devices to a certain extent. Therefore, exploring and researching p-type TCO thin film materials with good photoelectric properties has practical significance and wide application value.

NiO is a typical intrinsic p-type wide bandgap (3.7 eV) semiconductor material with a direct band gap. Both NiO and MgO have a cubic NaCl crystal structure with similar lattice constants. The lattice constant of NiO is 0.4177 nm, and that of MgO The lattice constant is 0.4212 nm, so theoretically any composition of Ni _1-x Mg _x O (O<x<1) infinite solid solution alloy film can be obtained. The band gap of MgO is 7.8 eV, and its band gap can be adjusted continuously by doping Mg in NiO, thus realizing its energy band engineering. However, the commonly prepared Ni _1-x Mg _x O alloy thin films exhibit high resistance, which largely limits their application as wide bandgap semiconductor materials in optoelectronic devices. Theoretical and experimental studies have shown that Li is an ideal acceptor doping element for NiO, so the hole carrier concentration can also be effectively increased theoretically by performing Li acceptor doping on Ni _1-x Mg _x O crystal thin films, Thereby reducing its resistivity and laying the foundation for the application of Ni _1-x Mg _x O thin films with continuously adjustable bandgap in short-wavelength optoelectronic devices. The pulsed laser deposition method has the advantages of easy control of deposition parameters, easy to keep the composition of the film consistent with the target, real-time doping and good quality of film crystals, etc., but so far no Li-doped p-type NiMgO crystals have been prepared by this method. Film reports.

Therefore, it is of great practical significance to develop Li-doped growth of p-type transparent conductive Ni _1-x Mg _x O crystal thin films.

Contents of the invention

The purpose of the present invention is to overcome the problems of existing p-type TCO film materials with few types and poor photoelectric performance so that it is difficult to meet the requirements of optoelectronic device applications, and to provide a Li-doped growth p-type transparent conductive Ni _1-x Mg _x O crystal film Methods.

The above-mentioned purpose of the present invention is achieved through the following technical solutions.

A method for Li-doped growth p-type transparent conduction Ni _1-x Mg _x O crystal thin film, its described method adopts pulsed laser deposition method, and its method step is as follows:

1) Weigh NiO, MgO and Li ₂ CO ₃ powders with a purity ≥99.99%, where the molar percentage x of Mg is 0<x<40, and the molar percentage y of Li is 0<y<10%. The above-mentioned powders are ball-milled and mixed uniformly, then pressed into shape, pre-sintered at 800 °C for more than 1 hour, and then sintered at 1100-1200 °C for more than 4 hours to prepare a Li-doped Ni _1-x Mg _x O ceramic target;

2) Put the ceramic target prepared in step 1) and the substrate after ultrasonic cleaning with acetone, ethanol and deionized water in sequence and blow dry with nitrogen into the growth chamber of the pulsed laser deposition device, the distance between the target and the substrate The distance is 4-6 cm, the vacuum degree of the back and bottom of the growth chamber is evacuated to 10 ^-4 Pa, the substrate is heated to keep the temperature at 300-500 °C, the growth atmosphere is pure O ₂ , the control pressure is 0.1-20 Pa, and the laser frequency The growth time is 3~5 Hz, and the growth time is 20~120 min. After growth, it is cooled to room temperature to obtain Li-doped p-type transparent conductive Ni _1-x Mg _x O crystal thin film.

In the above technical solution, further additional technical features are:

The obtained Li-doped p-type transparent conductive Ni _1-x Mg _x O crystal film was in-situ annealed for 30 min under the protection of oxygen atmosphere, and then slowly cooled to room temperature.

The thickness of the Li-doped p-type transparent conductive Ni _1-x Mg _x O crystal thin film is 50-400 nm.

The said substrate is silicon, sapphire, glass or quartz.

Realize the method for a kind of Li doping growth p-type transparent conduction Ni _1-x Mg _x O crystal film provided by the present invention, be by adjusting the molar percentage content of doping Mg and Li, substrate temperature and growth atmosphere pressure, A p-type transparent conductive Ni _1-x Mg _x O crystal thin film with continuously adjustable bandgap with different doping concentrations is prepared. The thickness of the thin film is determined by the deposition time, laser operating voltage and repetition rate. Its advantages and positive effects are:

The method of the invention can realize real-time doping, and simultaneously realize continuous adjustment of the band gap and p-type doping during the growth process of the Ni _1-x Mg _x O crystal film.

The doping concentration of the method of the present invention can be controlled by adjusting the growth temperature and the molar percentages of Mg and Li in the target.

The method of the present invention is simple, and the prepared p-type thin film has excellent crystal quality, not only maintains the cubic NaCl crystal structure, does not generate phase separation, but also has low resistivity, high transmittance, high carrier mobility, and relatively high With good repeatability and stability, the obtained film has broad application prospects in the fields of transparent electronics and optoelectronic devices.

Description of drawings

FIG. 1 is a schematic diagram of a pulsed laser deposition device used in the present invention. In the figure: 1: laser; 2: growth chamber; 3: target; 4: substrate.

Fig. 2 is an x-ray diffraction (XRD) spectrum of the p-type Li-doped transparent conductive Ni _1-x Mg _x O crystal film according to Example 1 of the present invention.

Fig. 3 is the optical transmission spectrum of the p-type Li-doped transparent conductive Ni _1-x Mg _x O crystal thin film in Example 1 of the present invention.

Detailed ways

The specific embodiment of the present invention is further described below

Example 1

1) Weigh NiO, MgO and Li ₂ CO ₃ powders with a purity of 99.99%, wherein the molar percentage x of MgO is 20%, and the molar percentage y of Li is 4%. NiO, MgO and Li ₂ The mixed powder of CO ₃ and an appropriate amount of ethanol were sequentially poured into a ball mill jar equipped with agate balls, and placed on a ball mill for 24 hours of ball milling. There are two purposes of ball milling: one is to mix NiO, MgO and Li ₂ CO ₃ powders evenly to ensure the uniformity of the prepared target material; the other is to mix NiO, MgO and Li ₂ CO ₃ The powder is refined to facilitate the subsequent molding and sintering of the mixed powder.

After ball milling, the raw materials are separated and dried, and the resulting powder is ground and pressed into shape. Put the formed green body into a sintering furnace, pre-sinter at 800 °C for 1 hour, and then sinter at 1100–1200 °C for more than 4 hours to obtain Li-doped Ni _0.8 with a thickness of about 3 mm and a diameter of 50 mm. Mg _0.2 O circular target.

2) Using the Li-doped Ni _0.8 Mg _0.2 O circular target as the target, the quartz substrate that was ultrasonically cleaned with acetone, ethanol and deionized water and dried with nitrogen was fixed on the sample stage in the pulsed laser deposition device , adjust the distance between the substrate and the target to 5 cm, and separate the substrate and the target with a baffle. The background vacuum in the growth chamber was evacuated to 10 ^-4 Pa, and then the substrate was heated to make the substrate temperature 400 °C, with pure O ₂ (purity 99.99%) as the growth atmosphere, the O ₂ pressure was controlled at 5 Pa, and the pulse laser energy The laser frequency was 300 mJ, the laser frequency was 5 Hz, the target was pre-sputtered for 10 min to remove the surface contamination of the target, and then the baffle was unscrewed to start deposition and growth. The growth time was 60 min, and the film thickness was 200 nm. The grown film was in-situ annealed for 30 min under the protection of an oxygen atmosphere, and then slowly cooled to room temperature to obtain a Li-doped Ni _0.8 Mg _0.2 O crystal film. Its x-ray diffraction (XRD) spectrum is shown in accompanying drawing 2, and its optical transmission spectrum is shown in accompanying drawing 3.

The prepared Li-doped Ni _0.8 Mg _0.2 O crystal thin film exhibits p-type conductivity and has excellent photoelectric properties at room temperature: the resistivity is 23.48Ω cm, the mobility is 0.61 cm2V ^-1 s ^-1 , and the hole concentration It is 4.35×10 ¹⁷ cm ^-3 , the average transmittance of visible light exceeds 70%, the optical band gap is about 3.9 eV, and the optoelectronic properties of the film do not change significantly after being placed for several months.

Example 2

1) Weigh NiO, MgO and Li ₂ CO ₃ powders with a purity of 99.99%, wherein the molar percentage x of MgO is 30%, and the molar percentage y of Li is 8%. NiO, MgO and Li ₂ The mixed powder of CO ₃ and an appropriate amount of ethanol were sequentially poured into a ball mill jar equipped with agate balls, and placed on a ball mill for 24 hours of ball milling. There are two purposes of ball milling: one is to mix NiO, MgO and Li ₂ CO ₃ powders evenly to ensure the uniformity of the prepared target material; the other is to mix NiO, MgO and Li ₂ CO ₃ The powder is refined to facilitate the subsequent molding and sintering of the mixed powder.

After ball milling, the raw materials are separated and dried, and the resulting powder is ground and pressed into shape. Put the formed green body into a sintering furnace, pre-sinter at 800 °C for 1 hour, and then sinter at 1100–1200 °C for more than 4 hours to obtain Li-doped Ni _0.7 with a thickness of about 3 mm and a diameter of 50 mm. Mg _0.3 O circular target.

2) With the Li-doped Ni _0.7 Mg _0.3 O circular target as the target, the sapphire substrate that was ultrasonically cleaned with acetone, ethanol and deionized water and dried with nitrogen was fixed on the sample stage in the pulsed laser deposition device , adjust the distance between the substrate and the target to 4 cm, and separate the substrate and the target with a baffle. The background vacuum in the growth chamber was evacuated to 10 ^-4 Pa, and then the substrate was heated to make the substrate temperature 500 °C, with pure O ₂ (purity 99.99%) as the growth atmosphere, the O ₂ pressure was controlled at 20 Pa, and the pulse laser energy The laser frequency was 300 mJ, the laser frequency was 5 Hz, the target was pre-sputtered for 10 min to remove the surface contamination of the target, and then the baffle was unscrewed to start deposition and growth. The growth time was 15 min, and the film thickness was 50 nm. The grown film was annealed in situ for 30 min under the protection of oxygen atmosphere, and then cooled slowly to room temperature to obtain a Li-doped Ni _0.7 Mg _0.3 O crystal film.

The prepared Li-doped Ni _0.7 Mg _0.3 O crystal thin film exhibits p-type conductivity and has excellent photoelectric properties at room temperature: the resistivity is 1268Ω·cm, the mobility is 537 cm2V ^-1 s ^-1 , and the hole concentration is 9.16×10 ¹² cm ^-3 , the average transmittance of visible light exceeds 65%, the optical band gap is about 4.1 eV, and the optoelectronic properties of the film do not change significantly after being placed for several months.

Example 3

1) Weigh NiO, MgO and Li ₂ CO ₃ powders with a purity of 99.99%, wherein the molar percentage x of MgO is 10%, and the molar percentage y of Li is 4%. NiO, MgO and Li ₂ The mixed powder of CO ₃ and an appropriate amount of ethanol were sequentially poured into a ball mill jar equipped with agate balls, and placed on a ball mill for 24 hours of ball milling. There are two purposes of ball milling: one is to mix NiO, MgO and Li ₂ CO ₃ powders evenly to ensure the uniformity of the prepared target material; the other is to mix NiO, MgO and Li ₂ CO ₃ The powder is refined to facilitate the subsequent molding and sintering of the mixed powder.

After ball milling, the raw materials are separated and dried, and the resulting powder is ground and pressed into shape. Put the formed green body into a sintering furnace, pre-sinter at 800 °C for 1 hour, and then sinter at 1100–1200 °C for more than 4 hours to obtain Li-doped Ni _0.9 with a thickness of about 3 mm and a diameter of 50 mm. Mg _0.1 O circular target.

2) The Li-doped Ni _0.9 Mg _0.1 O circular target was used as the target, and the glass substrate was ultrasonically cleaned with acetone, ethanol and deionized water and dried with nitrogen gas and fixed on the sample stage in the pulsed laser deposition device. , adjust the distance between the substrate and the target to 6 cm, and separate the substrate and the target with a baffle. The background vacuum in the growth chamber was evacuated to 10 ^-4 Pa, and then the substrate was heated to make the substrate temperature 300 °C, with pure O ₂ (purity 99.99%) as the growth atmosphere, the O ₂ pressure was controlled at 0.1 Pa, and the pulse laser energy The laser frequency was 300 mJ, the laser frequency was 5 Hz, the target was pre-sputtered for 10 min to remove the surface contamination of the target, and then the baffle was unscrewed to start deposition and growth. The growth time was 120 min, and the film thickness was 400 nm. The grown film was in-situ annealed for 30 min under the protection of an oxygen atmosphere, and then slowly cooled to room temperature to obtain a Li-doped Ni _0.9 Mg _0.1 O crystal film.

The prepared Li-doped Ni _0.9 Mg _0.1 O crystal thin film exhibits p-type conductivity and has excellent photoelectric properties at room temperature: the resistivity is 111Ω cm, the mobility is 30.5 cm2V ^-1 s ^-1 , and the hole concentration is 1.84×10 ¹⁵ cm ^-3 , the average transmittance of visible light exceeds 60%, the optical band gap is about 3.8 eV, and the optoelectronic properties of the film do not change significantly after being placed for several months.

Claims (2)

1. a Li doped growing p type electrically conducting transparent Ni _1-xmg _xthe method of O crystal film, comprises pulsed laser deposition, and its concrete grammar step is as follows:

1) by NiO, MgO and Li of purity>=99.99% ₂cO ₃powder, wherein the molar content x of Mg is 0<x<40%, the molar content y of Li is 0<y<10%, ball milling mixes rear compression moulding, 800 ° of C presintering more than 1 hour, more than 4 hours are sintered again, the obtained Ni mixing Li at 1100 ~ 1200 ° of C _1-xmg _xo ceramic target;

2) by above-mentioned steps 1) the obtained Ni mixing Li _1-xmg _xo ceramic target with insert in the growth room of pulsed laser deposition device with the substrate that nitrogen dries up with acetone, ethanol and deionized water successively ultrasonic cleaning, the distance adjusted between target and substrate is 4 ~ 6 cm, and growth room's back end vacuum tightness is 10 ^-4pa, substrate heating temperature is 300 ~ 500 ° of C, is the O of 99.99% with purity ₂for growth atmosphere, controlling pressure is 0.1 ~ 20 Pa, and laser frequency is 3 ~ 5 Hz; growth time is 20 ~ 120 min, grows, in-situ annealing 30 min under oxygen atmosphere protection; after be cooled to room temperature, obtaining thickness is the Li doped p type electrically conducting transparent Ni of 50 ~ 400 nm _1-xmg _xo crystal film.

2. method according to claim 1, substrate described in it is silicon, sapphire, glass or quartz.