第31卷 第1期
2008年2月
电子器件人才用英语怎么说
Chine J ournal Of Elect ron Devices
Vol.31 No.1Feb.2008
High Q uality G a N Display Films G row th on Pre 2T reated Sapphire Substrate 3
P EN G Dong 2sheng
1,2,3
,F EN G Yu 2chun 3,N I U H an 2ben 3,L I U X i ao 2f eng
3
1.X ian I nstit ute of Optics and Precision Mechanics ,Chine A cadem y of S ciences ,X i ′an 710068,Chi na;
2.Graduate School of t he Chine A cadem y of Sciences ,B ei j ing 100049,China;
3.I nstit ute of Optoelect ronics S henz hen Uni versit y ,S henz hen 518060,China
Abstract :Etch pit s on sapp hire substrate surface are formed after surface treating.GaN films have been grown by L P 2MOCVD on t he sapp hire subst rate ,which a half of it is pret reated by chemical etch.The crystal quality and optical quality of GaN films are analyzed by high 2resolution double crystal X 2ray rocking curve (XRC )and optical transmission measurement.The result s indicate t hat t he crystal quality of GaN determined by t ransmission measurement is in agreement wit h t hat determined by XRC ,t hat t he (0002)plane and (101-
大耳朵英语网站2)plane f ull 2widt h at half 2maximum by XRC of GaN films grown on p re 2t reated sapp hire substrate are as low as 208.80arcc and 320.76acrc ,respectively.The t ransmission spect rum of GaN is st udied to asss t he crystal and optical quality.The epilayer grown on pre 2t reated sapp hire substrate ex 2hibit s excellent optical quality ,in which t he yellow luminescence (Y L )is nearly invisible in t he p hotolumi 2nescence (PL )spect rum.The epilayer grown on t he pre 2t reated sapp hire subst rate exhibit s superior opti 2cal p roperties and crystal p roperties ,in which t he higher t ransmission ratio and t he greater modulation dept h can be shown in t he t ransmission spect rum.K ey w ords :MOCVD ;surface t reated ;GaN film EEACC :0520;2520D
预处理蓝宝石衬底上生长高质量G a N 显示薄膜3
彭冬生1,2,3，冯玉春3，牛憨笨3，刘晓峰3
1.中国科学院西安光学精密机械研究所，西安710068;
2.中国科学院研究生院，北京100049;
3.深圳大学光电子学研究所，深圳518060
收稿日期:2007204230
基金项目：广东省自然科学基金(04300863)；广东省关键领域重点突破项目(2B2003A107)；深圳市科技计划项目(200515)作者简介：彭冬生(19782)，男，中国科学院西安光学精密机械研究所博士研究生，主要从事光电材料与器件,pengdongsheng @;
the lucky one牛憨笨(19402)，男，博士生导师，研究员，中国工程院院士,HBNiu @szu.edu.
摘 要：采用化学方法腐蚀部分c 2面蓝宝石衬底，在腐蚀区域形成一定的图案，利用L P 2MOCVD 在此经过表面处理的蓝宝
石衬底上外延生长G aN 薄膜。采用高分辨率双晶X 射线衍射(DCXRD )、光致发光光谱(PL )、透射光谱分析G aN 薄膜的晶体质量和光学质量。分析结果表明,G aN 薄膜透射谱反映出的GaN 质量与X 射线双晶衍射测量的结果一致，即透射率越大，半高宽越小，结晶质量越好；对蓝宝石衬底进行前处理可以大大改善G aN 薄膜的晶体质量和光学质量，其(0002)面及(101-
2)面
XRD 半高宽(FW HM )分别降低到208.80arcc 及320.76arcc ，而且其光致发光谱中的黄光带几乎可以忽略。
关键词:MOCVD ；表面处理;GaN 薄膜中图分类号:TN 304.055
文献标识码:A 文章编号:100529490(2008)0120057204
The wide variety of potential applications of III 2V nit ride miconductors have drastically pro 2
moted t he rearch activity related to t he materi 2
als.Especially ,t he demonst ration of bright blue
light emitting diodes(L EDs)and blue lar diodes (LDs)has proven nit ride2bad miconductors to be a promising material system for high2power and high2speed optoelect ronic display devices[122].Al2 t hough dramatic p rogress has been made in impro2 ving bot h epitaxial material quality and device per2 formance,substantial challenges remain.In parti2 cular,t he lack of readily available homoepitaxial substrates typically necessitates growt h on sap2 p hire,which lead to degradation in material quality p redominantly t hrough t he prence of high densi2 ties of t hreading dislocations.Threading disloca2 tions in GaN degrade device performance t hrough carrier scattering[3],nonradiative recombina2 tion[4],and incread rever2bias leakage cur2 rent[526].Many met hods are adopted in order to de2 crea dislocatio n density,t he mo st uf ul met hod is epitaxial lateral overgrown(ELO)technique, and t his technique can result in dislocation density veral orders magnit ude lower t han in t he planar GaN hetero st ruct ures[7].However,as already known,t he ELO technology requires a relatively complicated p rocedure,and t he mask is ud in t he conventional ELO technique generally,moreover, interaction of t he wings wit h t he mask underneat h is commonly obrved in ELO struct ures.This p heno menon leads to a downward tilt of t he ELO wings and to creation of low angle boundaries over t he mask edges as well as causing p ro blems for de2 fect2f ree coalescence of tilted wings grown f rom ad2 jacent eds[8210].In t his paper,high quality GaN films wit h low dislocation density have been grown on s
app hire subst rate by surface t reat ment in order to overcome t ho p roblems existing in t he conven2 tional ELO technique.
1 Experimental Procedure
In t his st udy,a c2plane(0001)2oriented single polished2”sapp hire substrate is ud.A half of t he sapp hire subst rate is etched chemically in t he molten KO H solvent at250℃～350℃lasting for 30min～60min,so t he sapp hire substrate is divided into two part s,namely etched part and common part,t hen it is cleaned by aceto ne to wipe off or2 ganism on t he subst rate.
The growt h of GaN films are carried out in a vertical rotating disk MOCVD reactor manufac2 t ured by Thomas Swan Scientific Equip ment Limit2ed Company at a p ressure of100Torr.The pre2 t reated subst rate is initially annealed in H2at mos2 p here at1000℃,t hen t he temperat ure is decread to525℃for t he growt h of buffer layer,followed by undoped GaN layer grown at1060℃,t hen in2 creasing t he ratio of V/III in order to laterally grow even and high quality GaN films.V/III ratio is incread by decreasing t he flow rate of t rimet h2 ylgallium(TM Ga),and t he flow rate of ammonia (N H3)is identical for t he whole process.The total epitaxial layer t hickness is about3μm.In all of t he above cas,t he TM Ga and N H3are ud as p recursors,and hydrogen(H2)as a carrier gas.
bleach什么意思Crystallograp hic p roperties are evaluated by (0002)and(101
-
2)high resolution double crystal X2ray diffraction curve(XRC)measurement using a four2crystalline Philip XRC system.The surface morp hology is characterized by an atomic force mi2 cro scopy(A FM)using SPI3800N.The excitation of t he GaN films is made for PL of RPM2000by means of266nm fourfold f requency Nd:YA G La2 r.GaN films t ransmission spectrum is measured by p hotometer of Lambda800/900.
2 R esults and Discussion
Figure1(a)shows the surface microscopy of pre2 treated sapphire substrate.Since there is some dislocation on sapphire substrate,and the chemical etch velocity in the regions with dislocation concentra2 tion is faster than that in el place,some etch pits are formed in tho regions with dislocation concentration. Whereas,the etching velocity in el regions is aniso2 tropic,too,so some micro2sidesteps are formed,as shown figure1(a).The etch pits en from figure1 (a)are likely to be convex,but in fact,the are con2 cave.Figure1(b)clearly shows the etching pits mi2 croscopy of treaded sapphire
surface.
(a)The surface microscopy of pre2treated sapphire substrate
中秋节翻译
85电 子 器 件第31卷
(b )The microscopy of etch pits on substrate surface
Fig.1 The microscopy of sapphire surface
For simplicity ,t he GaN grown on t he chemi 2cally etched part of t he sapp hire subst rate is deno 2t
ed as sample A ,and t he GaN grown on t he com 2mon part as sample B.In order to compare t he crystal quality ,(0002)and (101-
2)X 2ray diff rac 2tion curve (XRC )measurement s are carried out on t he samples ,in which t he f ull widt h at half max 2imum (FW HM )of t he diff raction peak can show t he magnit ude of screw dislocation and edge dislo 2cation ,respectively.The XRC of sample A and sample B are shown
in Figure 2.The FW HMs
of
(a ) (0002)plane
(b ) (101-
2)plane
Fig.2 The XRC of sample A 、B
sample B in (0002)plane and (101-
2)plane are
281.16arcc and 467.64arcc ,respectively ,while t ho of sample A are decread to 208.80arcc and 320.76arcc ,respectively.So t he dis 2location density of GaN epilayer can be greatly re 2duced in t he ca of using chemically etched sap 2p hire
substrate.
The sharp cutoff and Fabry 2Perot oscillations
Fig.3 Optical transmission spectrum of G aN
of t he t ransmission spect ra for t he GaN films ,shown in Figure 3,confirm t he high quality films.The optical absorption edge of GaN films is at 365nm ,corresponding wit h t he fact t hat t he bandgap of GaN is 3.4ev.Wit h t he improvement of GaN films crystal quality ,t he dispersion for t he incidence is decread ,t he absorption for incidence is reduced too ,t he transmission ratio has been in 2cread greatly.The t ransmission ratio of sample A is greater t han t hat of sample B ,as shown in figure 3.This result is in good agreement wit h t he struct ure analysis ,which disclod t he lower XRC FW HMs for sample A.And t he modulation dept h of optical t ransmission spectrum for sample A is greater ,compared wit h t hat for sample B ,t he op 2tical quality of sample A is superior to t hat of sam 2ple B.
Room temperat ure p hotoluminescence (PL )spect ra of GaN epilayers are shown in figure 4.The PL intensity of sample A is st ronger t han t hat of sample B ,t he FW HM of sample B is 14.2nm ,whereas t hat of sample A is decread to 8.2nm.The Y L of t he sample B is st ronger ,while t hat of
t he sample A is nearly invisible in t he PL spec 2t rum.The GaN epilayer wit h high quality exhibit s almost no Y L emission.Alt hough t he origin of t he Y L is still being debated ,it is well acknowledged t hat t he Y L corresponds to t he deformed crystal struct ure.In our work ,it ems t hat t he Y L is re 2lated to t he dislocation.The intensity of t he near band edge PL emission of GaN is indicative of it s optical quality.So sample A has a higher optical quality ,compared wit h sample B ,which corre 2sponds wit h t he higher crystal quality of sample A concluded by t he above discussion.The experi 2mental result s show t hat t he optical quality of GaN determined by PL is in agreement wit h t hat deter 2mined by t ransmission measurement.
9
5第1期彭冬生，冯玉春等：预处理蓝宝石衬底上生长高质量GaN 显示薄膜
Fig.4 Photoluminescence spectra of GaN epilayers
The growt h condition of sample A and sample B is same absolutely except t hat sample A has been grown on p re2t reated part of sapp hire subst rate, sample B grown on common part of t he same sap2 p hire subst rate.Whereas,t he dislocation density of sample A is lower t han t hat of sample B,t he crystal and optical quality of sample A are superior to t ho of sample B.Therefore,t he crystal an
d optical quality of epilayer can be improved and dis2 location density can be decread by surface t reated sapp hire subst rate.
卖服装的语言技巧Some micro2sidestep s t hat are formed in t he regions where t here is not etching pit s are helpf ul to nucleate in t he cour of growt h.The vapor p ha epitaxy start s f rom t he regions where t here is not etching pit s,whereas nucleation is formed on t he pit s,nevert heless t he nucleation velocity is too slow,and it is more and more slow wit h t he in2 crea of pit dept h o n t he same pit.The ratio of t he lateral growt h velocity to t he vertical growt h velocity increas by increasing V/III ratio,t hen two wings coalesce o n t he etch pit s to give a uni2 form film.The etch pit s can slacken part lattice mismatch between GaN epilayer and sapp hire sub2 strate,and part of dislocation bending in t he con2 quent process of lateral growt h renders it not to reach GaN films surface,so t he dislocation density can be decread drastically.The hollow st ruct ure of etch pit s can partly relea stress of GaN films to improve t he quality of GaN films.
3 Conclusion
In summary,t he epilayer grown on t he p re2 t reated part of sapp hire subst rate exhibit s superior optical p roperties and crystal properties,in which t he(0002)plane and(101
-
陷阱英语
2)plane f ull2widt h at half2maximum by XRC of GaN films grown on pre2 t reated sapp hire subst rate are as low as208.80 arcc and320.76acrc,and t he yellow lumines2 cence is nearly invisible in t he p hotoluminescence spect rum,t he higher transmission ratio and t he greater modulation dept h can be shown in t he t ransmission spect rum.
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06电 子 器 件第31卷
