CN104790033A - Method for growing high-quality ZnO thin-film material on ZnO single-crystal substrate at low temperature - Google Patents
Method for growing high-quality ZnO thin-film material on ZnO single-crystal substrate at low temperature Download PDFInfo
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Abstract
A method for growing a high-quality ZnO thin-film material on a ZnO single-crystal substrate at low temperature comprises steps as follows: (1), a ZnO single crystal is selected to serve as a growth substrate, and a Zn polar surface is selected to serve as the growth substrate; (2), the substrate is pretreated; (3), low-temperature growth of a ZnO thin film is performed, the surface temperature of the substrate is 400 DEG C-500 DEG C, dimethyl zinc and tertiary butanol are adopted to serve as a zinc source and an oxygen source respectively, high-purity nitrogen serves as carrier gas and diluent gas, the flow speed of DMZn and the flow speed of t-BuOH are 10-40 SCCM and 100-400 SCCM respectively, the pressure of a reaction cavity is 15-30 kPa in the growth process, and the thickness of the film is determined by the growth time which is usually 15-60 min; (4), proper in-site thermal treatment is performed on the growing ZnO thin film.
Description
Technical field
The present invention relates to semiconductor material growing technical field, is the method utilizing metal organic source chemical vapor deposition (MOCVD) equipment to prepare high quality ZnO film in zinc oxide (ZnO) single crystalline substrate.
Background technology
GaN film material, as the outstanding representative of third generation semiconductor material, is used widely in brightness blue light luminescence/Laser Devices.The ZnO film all very close with GaN film structure and properties also receives the concern of people always.Compared to GaN, the exciton bind energy of ZnO material, up to 60meV, is about 2.5 times of GaN, under this also just determines room temperature, exciton can in ZnO system stable existence.Therefore ZnO is also the preferred material of room-temperature exciton type ultraviolet/visible luminescent/Laser Devices.But because high quality p-type ZnO fails to break through all the time, this outstanding physical properties of ZnO temporarily could not embody.Sapphire Substrate due to its lattice consistent with GaN/ZnO, and lattice mismatch is relatively little, is widely used for the growth substrates doing GaN/ZnO film always.But due to surface reaction, lattice mismatch and coefficient of thermal expansion mismatch etc., the ZnO material grown on a sapphire substrate faces the problems such as high defect, dislocation desity, heavily stressed, substrate film element mutual diffusion all the time.So, utilize ZnO bulk-shaped monocrystal to do substrate and carry out iso-epitaxy and just can avoid these problems.Compared to the disappearance of GaN bulk-shaped monocrystal, ZnO monocrystalline has easy, ripe technology of preparing, is therefore also with a wide range of applications to the research of homogenous growth ZnO film on ZnO monocrystalline.
Extension homogeneity film in ZnO single crystalline substrate, due to the crystal mass significantly improved, optics, the electric property of film also will be greatly improved.But because c face ZnO exists two kinds of polarity, on the monocrystalline of these two kinds of polar surface, the film crystal quality of extension and optical and electrical properties have a great difference.Such as, on Zn face ZnO monocrystalline, the roughness of film of extension is low, and grain-size is large, and border is few, and the extension on the monocrystalline of Zn face is closer to two-dimensional growth; And for example on Zn face, nitrogen (N) doping efficiency of epitaxial film is higher, and involuntary impurity, as mixing of carbon (C) can be inhibited on the contrary; For another example due to stronger exciton phonon coupling, on Zn face, the photoluminescence intensity of epitaxial film can reach 30 times of the film of same extension of conditions on the monocrystalline of O face.The difference of the surface kinetics reaction mechanism that these differences cause from dangling bonds quantity variance on two kinds of faces to a great extent.Except the difference of polar surface, the preconditioning technique of substrate also can change the surface of single crystalline substrate, and then changes quality and the character of epitaxial film thereon.There are some researches show, the cut, damage etc. of single-crystal surface are by about 1000 DEG C O
2thermal treatment in atmosphere obtains very large reparation.Pre-treatment can also form atom level step at substrate surface, is conducive to the two-dimensional layer growth of epitaxial film.Therefore the suitable quality of substrate pre-treatment technology to epitaxial film is most important.
For the hetero epitaxy of ZnO, lattice quality and doping efficiency are a pair implacable contradiction all the time.In order to pursue doping efficiency, growth must be carried out at a lower temperature.But low-temperature epitaxy determines its growth mechanism by surface kinetics process, adatom is low at substrate surface transfer ability, is easy to cause three-dimensional island growth pattern, introduces involuntary impurity; Simultaneously in order to discharge stress, certainly lead to the defect of high density, dislocation, fault.Obtain high-quality film, just must adopt the growth under higher underlayer temperature, but at high temperature, foreign atom solid solubility is extremely low, almost can not realize Effective Doping, and high temperature service energy consumption is huge, design is complicated, and production cost promotes; Due to high-temperature technology, make the integrated poor compatibility of other devices of ZnO film made.As can be seen here, the research of low temperature growth techniques is very crucial to the practical application of ZnO film, and utilizes the iso-epitaxy in ZnO single crystalline substrate, can the above-mentioned contradiction of active balance.Owing to there is not stress and mismatch, even if at a lower growth temperature, be aided with situ heat treatment technology after suitable growth, also can obtain the ZnO monocrystal thin films of very high-quality, this is in hetero epitaxy, is extremely difficult realization in such as, ZnO film in Sapphire Substrate.Lower growth temperature also makes the present invention be easy to be applied in all kinds of ZnO thin film doped preparation.
Summary of the invention
The object of the invention is, provide a kind of in ZnO single crystalline substrate, utilize MOCVD device, prepare the technology of high quality ZnO film at a lower growth temperature.
In ZnO single crystalline substrate, the method for low-temperature epitaxy high quality ZnO film material, comprises the steps:
1) ZnO monocrystalline is chosen as growth substrates; Choose the ZnO monocrystalline of suitable polar surface, described suitable polar surface is that Zn polar surface [i.e. (0001) face] is as growth substrates;
2) pre-treatment is carried out to substrate;
3) low-temperature epitaxy of ZnO film is carried out; Substrate surface temperature 400 DEG C – 500 DEG C, adopts zinc methide (DMZn) and the trimethyl carbinol (t-BuOH) to make zinc source and oxygen source respectively, high pure nitrogen (N
2) make carrier gas and carrier gas, the flow velocity of DMZn and t-BuOH is respectively 10-40SCCM and 100-400SCCM, and in process of growth, reaction chamber pressure is 15 – 30kPa; Growth time determines the thickness of film, and general growth time is 15 – 60min;
4) carry out suitable situ heat treatment to the ZnO film of growth, after referring to that ZnO film growth terminates, the heat treatment process that original position is carried out ZnO film, thermal treatment temp is 800 – 900 DEG C, and process atmosphere is N
2o, N
2o flow velocity is 0.5 – 2SLM, and chamber pressure is 15 – 30kPa, and heat treatment time is 2 – 5min.
Further, described pre-treatment, refer to that pretreatment temperature is 900 – 1100 DEG C, Pretreatment atmosphere is N
2o, N
2o flow velocity is 0.5 – 2SLM, and chamber pressure is 15 – 30kPa, pretreatment time 4 – 6min;
Concrete, described lower growth temperature, refers to substrate surface temperature less than 500 DEG C.
Beneficial effect of the present invention:
1) utilize three dangling bonds of O atom on ZnO single crystalline substrate Zn face to the stable binding of adsorbing Zn atom or Zn-O group, realize the smooth growth of two dimension of ZnO film;
2) the smooth growth of the two dimension of ZnO film, film is made to have less ZnO grain boundary, under hydrocarbon (CH) group being conducive to being adsorbed on growth surface has more time and larger probability to be exposed to O atom atmosphere, reaction generates gaseous carbon oxide, thus reaches the effective suppression to carbon (C) related impurities in growing ZnO thin-film;
3) utilize the pre-treatment to ZnO single crystalline substrate, contribute to repairing substrate surface damage, realize the atom level step of growth surface, be conducive to the nucleation of adatom in process of growth, and then be conducive to the two-dimensional growth of film;
4) the ZnO film growth temperature of less than 500 DEG C can make doping become to be more prone to, also significantly can to reduce the energy consumption in preparation process, reduces equipment complexity, improves device compatible, is conducive to production control cost, more energy-conserving and environment-protective;
5) the ZnO film situ heat treatment after having grown, treatment temp is set under the prerequisite not causing ZnO film Surface disintegration, be conducive to promoting the migration of atom in film lattice, thus improve membrane structure and optical quality and lifting c-axis preferred orientation further.
Accompanying drawing explanation
Fig. 1 is the preparation flow figure of high quality ZnO film in the present invention.
Fig. 2 is atomic force microscopy (AFM) figure of high quality ZnO film in the present invention, in order to surface topography and the roughness of characterizing sample, wherein Fig. 2 (a) is in 1000 DEG C of pretreated Zn face ZnO single crystalline substrate, grows 30min and scheme through the AFM of the ZnO film of outgrowth postheat treatment 3min under 470 DEG C of underlayer temperatures; Fig. 2 (b) is in 1000 DEG C of pretreated O face ZnO single crystalline substrate, grows 30min and scheme through the AFM of the ZnO film of outgrowth postheat treatment 3min under 470 DEG C of underlayer temperatures; Fig. 2 (c) is in 1000 DEG C of pretreated Zn face ZnO single crystalline substrate, grows the AFM figure of the ZnO film of 30min under 850 DEG C of underlayer temperatures.
Fig. 3 grows on 900 DEG C of pre-treatment ZnO monocrystalline, the X-ray diffraction rocking curve figure of all the other conditions 3 samples as described in Fig. 2 (a), 2 (b), 2 (c).
Fig. 4 grows on 900 DEG C of pre-treatment ZnO monocrystalline, the Raman scattering spectra of all the other conditions 2 samples as described in Fig. 2 (a) and 2 (b).
In Fig. 5, two spectral lines are the Photoluminescence of 2 samples as described in Fig. 2 (a) and 2 (b) respectively.
Embodiment
The invention provides a kind of polar surface by ZnO single crystalline substrate to select and pre-treatment, be aided with growth postheat treatment, utilize the MOCVD device extension method of ZnO film at a lower growth temperature, the thin film of the method growth, for high lattice quality, low impurity concentration and good optical, electrical character, can be used as the buffer layer of further high growth temperature ZnO epitaxial film; The present invention is also the ZnO thin film doped basic technology of study of various.In order to make object of the present invention, method and advantage clearly understand, below in conjunction with specific embodiment, and with reference to accompanying drawing, the present invention is described in more detail.Concrete, described MOCVD device, preferably needs to possess vertical spray head air intake structure.
Accompanying drawing 1: implementation step schema of the present invention, wherein contains 7 main steps:
Step 1 (S1): select the c face ZnO monocrystalline of Zn polar surface as the epitaxially grown substrate of ZnO film;
Step 2 (S2): substrate is cleaned, and be placed on the graphite pallet of MOCVD device, the wash procedure of sample is as follows:
(1) substrate is placed in clean small beaker;
(2) repeatedly rinse with a large amount of deionized water;
(3) acetone soln is added as in beaker, and ultrasonic cleaning 10min;
(4) by acetone soln to the greatest extent, excessive straight alcohol is added, ultrasonic cleaning 10min;
(5) repeatedly substrate is rinsed with a large amount of deionized waters;
(6) dry up with high pure nitrogen.
Step 3 (S3): utilize molecular pump and the dry pump of prime to vacuumize reaction cavity, until chamber pressure is down to 3E-3Pa, carry out the preparation before substrate pre-treatment;
Step 4 (S4): open N
2o gas cylinder, control reducing valve to suitable pressure, and open the air circuit breaker leading to cavity from gas cylinder, adjustment mass flowmeter, to 0.5 – 2SLM, by the valve between air pump and cavity, controls cavity pressure-stabilisation to 15 – 30kPa, by radio-frequency induction heating power supply and coil, graphite pallet is heated, and be warming up to 900 – 1100 DEG C, keep 4 – 6min, thermal pretreatment is carried out to ZnO single crystalline substrate; ZnO single crystalline substrate is placed in graphite pallet;
Step 5 (S5): after pre-treatment terminates, reduces underlayer temperature and controls underlayer temperature in 400 –, 500 DEG C of embodiments and get 420 and 480 DEG C, close N afterwards
2o gas circuit, opens high-purity N
2cushion gas and carrier gas gas circuit, control cavity pressure-stabilisation to 15 – 30kPa, open DMZn and t-BuOH organic source steel cylinder, and pass into high-purity N
2carrier gas, remain on 10 – 40SCCM by mass flowmeter adjustment DMZn gas circuit flow, t-BuOH gas circuit flow is 100 – 400SCCM, and in embodiment, t-BuOH is ten times of DMZn, makes the pressure-controlling of growth chamber at 15 – 30kPa.Pass through pressure valve gate control two steel cylinder pressure to 1atm in bypass, after organic source flux and pressure-stabilisation, two-way gas is cut reaction chamber from bypass, start the epitaxy of ZnO film, behind 15,30 or 60min, obtain the film of different thickness; Close cylinder valve and the high-purity N in the organic source of DMZn and t-BuOH
2carrier gas, terminates growth;
Step 6 (S6): close high-purity N one by one
2cushion gas and carrier gas, reopen N
2o gas circuit, adjusts mass flowmeter to 0.5 – 2SLM, by the valve between air pump and cavity, control cavity pressure-stabilisation to 15 – 30kPa, by radio-frequency induction heating power supply, 800 – 900 DEG C is warming up to graphite pallet, keeps 2 – 5min, rear growth situ heat treatment is carried out to epitaxial film;
Step 7 (S7): after situ heat treatment terminates, closes radio-frequency induction heating power supply, after sample Temperature fall to room temperature, closes N
2o gas circuit, passes through high-purity N
2inflation makes reaction chamber recover normal atmosphere, opens cavity, takes out sample.
Fig. 2: Fig. 2 (a) and 2 (b) directly compared for the surface topography of extension sample in Zn polar surface and O polar surface.As can be seen from the figure, on Zn face, the sample of extension shows stratiform two dimensional mode, and surface crater is less and density is lower, and the r.m.s. roughness of this sample is 2.65nm; And the sample of extension shows island three dimensional growth mode on O face, surface undulation is obvious, pit is larger and close, and its r.m.s. roughness is 24.02nm.We analyze the difference that its mechanism is the dangling bonds quantity of Zn face and surface, O face O atomic shell.Zn polar surface surface O atom has 3 dangling bonds, and O polar surface surface O atom only has 1 dangling bonds.The number of dangling bonds quantity determines in process of growth the stability of adsorbing Zn atom or Zn-O molecule.The O atom in Zn face is more stable with the Cheng Jian of absorption Zn atom or Zn-O molecule, and adatom or molecule be mobile also conglomerate not easily, thus is conducive to stratiform two-dimensional growth; And O face O atom is relative unstable with their one-tenth key, adatom or molecule is made to tend to migrate to the step place of incipient nucleation sites and growth surface, because the one-tenth key atom of there has 2 dangling bonds, the growth at growth surface step place, faster than other positions, finally result in island three dimensional growth.Adatom or molecule also result in the growth velocity of Zn face film faster than O face film in the high desorption rate that the instability of growth surface is brought.Fig. 2 (a) and 2 (c) directly compared for same in Zn polar surface, the surface topography of growing film under various substrate.Shown in Fig. 2 (c), surface topography is similar to 2 (a), and its r.m.s. roughness is 2.86nm, suitable with the described sample of Fig. 2 (a).This just illustrates that the growth of lesser temps is aided with the technology growing rear situ heat treatment and can reaches the surface topography comparable with direct high temperature epitaxy and planeness completely.We think that its mechanism is the introducing of Zn polar surface ZnO single crystalline substrate.Although in low-temperature epitaxy, surface kinetics reaction mechanism determines the growth pattern of film, but there is not stress and mismatch problems due to iso-epitaxy, and the absorption of Zn face is stable, even if make also to obtain the dense film possessing flat surface at a lower growth temperature.
Fig. 3: the lattice quality carrying out characterizing sample further by X-ray diffraction rocking curve (XRC).The halfwidth of XRC curve is the important indicator weighing sample monocrystalline quality.As shown in Figure 3, on the substrate of Zn face, (0002) axle XRC halfwidth of the ZnO film of low-temperature epitaxy is 52.2arc sec, and on O face, (0002) axle XRC halfwidth of sample is 93.6arc sec.Therefore on Zn face, the monocrystalline quality of extension sample is more excellent.Narrow low defect, dislocation, fault and the impurity concentration brought owing to the iso-epitaxy in Zn polar surface to the XRC halfwidth of 52.2arc sec.We compared for the XRC of high temperature epitaxy sample on Zn face equally, and on its halfwidth and Zn face, low-temperature epitaxy sample quite (52.4arc sec).This also illustrates low-temperature epitaxy and be aided with the film that the technology growing rear situ heat treatment can obtain high lattice quality.Fig. 2 and Fig. 3 describes low temperature growth techniques of the present invention can obtain the surface comparable with high temperature epitaxy film and lattice quality.Compared to high temperature epitaxy, low-temperature epitaxy is with the obvious advantage, mainly declines in the equipment of guarantor complexity, preparation cost declines, equipment energy consumption declines, strengthens with the compatibility of other modules, system.More importantly, low-temperature epitaxy is conducive to effectively mixing of doping agent, thus realizes the realization of all kinds of doping film in ZnO single crystalline substrate.
Fig. 4: the lattice quality and the impurity behavior that utilize low-temperature epitaxy ZnO film on Raman spectral investigation Zn face and O face further.E in ZnO
2vibration modes characterizes the horizontal vibration of Zn-O key, wherein E
2and E (low)
2(high) sensitive to the vibration of Zn atom and O atom respectively, its intensity is often used to the behavior studying native defect in ZnO.The E of Zn face sample and O face sample is taken out from Fig. 4
2(high)/E
2(low) value is 0.50 and 0.46 respectively.Zn face sample has higher E
2(high)/E
2(low) value illustrates that the concentration of Lacking oxygen in this sample is lower than O face sample, illustrate that sample vacant lattice position, Zn face defect is less, and O/Zn stoicheiometry is more close to 1:1.In addition, at O face sample 1360 and 1585cm
-1also there are two peak bags in wave number place, these two peaks are from the involuntary doping carbon impurity in sample.As can be seen from Figure 4, the C peak in the sample of Zn face obtains good suppression.In MOCVD, in sample, generally containing the involuntary doping C of about 2%, this is because include CH group in metal organic source, when growth, if the CH group on surface can not get timely desorption, then can become impurity in the film that namely C atom enters growth.In the film of Zn face Grown, the suppression of C is relevant at the high desorption rate of growth surface with CH group.Look unfamiliar on long surface at smooth Zn, CH group has the O in more times and probability and growth atmosphere and H atom to react, and forms gaseous carbon oxygen or hydrocarbons.And the growth on O face, occur in step place owing to growing to concentrate, the CH group moving to step place almost has no time to go out growth surface with probability desorption, thus causes serious C impurity to mix.In addition because grain boundary defect concentration is high, the formation of C impurity at grain boundary place can be lower, and as can be seen from the surface topography shown in Fig. 2, Zn face film grain-size is very large, and there is grain boundary hardly, therefore C impurity not easily mixes; And O face film crystal grain is less, C impurity easily in grain boundary enrichment, thus causes the C impurity of higher concentration in film.The C impurity of grain boundary can cause the ununiformity of Thin film conductive, thus the serious electrical properties reducing film.Compared to high temperature epitaxy, low-temperature epitaxy, especially during Heteroepitaxy, mixing of C impurity is very general.Low-temperature epitaxy on the ZnO monocrystalline of Zn face of the present invention can effectively suppress mixing of C impurity.
Fig. 5: utilize Photoluminescence to have studied the optical property of growth ZnO film on Zn face and on O face.As can be seen from the figure, the nearly band-edge emission intensity of the ultraviolet of Zn face sample is far away higher than O face sample.This surface with kind of the sample of two described in Fig. 2, Fig. 3 and lattice quality consistent.Sample more weak nearly band edge in O face is luminous relevant to the non-radiative recombination center that defect and impurity in sample (as C) is introduced.Luminous zone in band, it is luminous that O face sample has stronger greenbelt, and the greenbelt of Zn face sample is detectable hardly.Consider described in Fig. 4, comparatively Zn face sample is high for the oxygen vacancy concentration of O face sample, and greenbelt is here luminous owing to the deep energy level radiation relevant to Lacking oxygen.Zn face sample possesses high nearly band-edge emission and without luminous in band, has absolutely proved that the method for the invention can prepare the ZnO film of high optical quality.
Claims (3)
1. the method for low-temperature epitaxy high quality ZnO film material in ZnO single crystalline substrate, is characterized in that comprising the steps:
1) ZnO monocrystalline is chosen as growth substrates; Choose the ZnO monocrystalline of suitable polar surface, described suitable polar surface is that Zn polar surface [i.e. (0001) face] is as growth substrates;
2) pre-treatment is carried out to substrate;
3) low-temperature epitaxy of ZnO film is carried out; Substrate surface temperature 400 DEG C – 500 DEG C, adopts zinc methide (DMZn) and the trimethyl carbinol (t-BuOH) to make zinc source and oxygen source respectively, high pure nitrogen (N
2) make carrier gas and carrier gas, the flow velocity of DMZn and t-BuOH is respectively 10-40 SCCM and 100-400 SCCM, and in process of growth, reaction chamber pressure is 15 – 30 kPa; Growth time determines the thickness of film, and general growth time is 15 – 60 min;
4) carry out suitable situ heat treatment to the ZnO film of growth, after referring to that ZnO film growth terminates, the heat treatment process that original position is carried out ZnO film, thermal treatment temp is 800 – 900
oc, process atmosphere is N
2o, N
2o flow velocity is 0.5 – 2 SLM, and chamber pressure is 15 – 30 kPa, and heat treatment time is 2 – 5 min.
2. the method for low-temperature epitaxy high quality ZnO film material in ZnO single crystalline substrate according to claim 1, it is characterized in that described pretreatment condition is, be 900 – 1100 DEG C in temperature, Pretreatment atmosphere is N
2o, N
2o flow velocity is 0.5 – 2 SLM, and chamber pressure is 15 – 30 kPa, pretreatment time 4 – 6 min.
3. the method for low-temperature epitaxy high quality ZnO film material in ZnO single crystalline substrate according to claim 2, it is characterized in that ZnO single crystalline substrate is placed in graphite pallet, by radio-frequency induction heating power supply and coil, graphite pallet is heated, be warming up to 900 – 1100 DEG C.
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| CN111948235A (en) * | 2020-08-07 | 2020-11-17 | 广西大学 | Method for measuring semipolar plane III group nitride film defect density and application thereof |
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| CN1622302A (en) * | 2004-10-25 | 2005-06-01 | 中国科学院物理研究所 | Three buffer layer method for preparing high quality zinc oxide monocrystalline film |
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| CN1622302A (en) * | 2004-10-25 | 2005-06-01 | 中国科学院物理研究所 | Three buffer layer method for preparing high quality zinc oxide monocrystalline film |
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| CN111948235A (en) * | 2020-08-07 | 2020-11-17 | 广西大学 | Method for measuring semipolar plane III group nitride film defect density and application thereof |
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