characterization of p and n-type bulk insb crystals grown ...nopr.niscair.res.in › bitstream ›...
TRANSCRIPT
I nci i ,Ill Journal of Purc & Arp li cd Physics Vol. JX. April 2(X)O. pp 2:17-242
Characterization of p and n-type bulk InSb crystals grown by vertical directional solidification technique
DB Gadkari
Dcpartmcnt of Physics. Mithiha i College. Mumhai 4(X) O.'i6
and
B M Arora
CM and MS. Tata Institute of Fundamental Research. Mumhai 400 OO.'i
Received 2.'i Novemher IlJl)l): rev iscd 10 February 2000
Crystal growth of undopcd and Te-doped InSh sing le crysta ls has heen achieved hy thc modified vert ica l directi onal
solidification (YDS) technique. T he grown crystnls of undoped growth are /Hype with carri er concentration and mohility of the
order of2.4 x IOl ll cm-·1
and .'i.e) x IO.l cm:: IVs at JOO K and 1.32 x 1016 cm- .1 and 3.4 x 10' cm 2, Ys al20 K. Te doped cryslab
;II"L' II -type wi th electron dcnsity (.'i.2 x 1017
cm- ' ) vi rtuall y remaining unchanged with temperature up to 20 K. Whil e mohilil y
has increased with dccre; lsc intcmpcraturc (3 x IO.l em2,ys at 2() K ). Growth morrhology reve,il s the eutectic micmstructurc\
hut heavi Iy Te-dorcd growth showed strimion. hand formation and preci pitation . T he quality of I nSh crysta ls have heen improved
hy the optim i7.ed growth conditi ons.
1 Introduction I/l -V compound semi conductor devices I and circuits
are becoming extensi vely important in optoelectronics applications". Fabrication of devices needs large size si ngle crystals ' . InSb has hi ghest electron mobilit/ among the ITI- V compound s. Growth of bulk JnSb single crysta l was done hy the modifi ed Czocharalski tec hnique" and low defect crystal s of ca rrier co ncentration I.') x 1() '7 CI11- ' have heen grown. Experiments were carried out in microgravit/ and usi ng centrifuge tech
niques 7, und oped crysta ls with mobility 2.5 x IO.l
CI11 2/VS and Te doped crystals of mobility 3.7 x 10' cm2/Vs had also been grow n. InSb crystals were also grown hy hori zontal Bridgemanx
• vertical Bridgeman , verti ca l gradient freeze tec hnique ' 4 and submerged heater methoc\') hut crystal s were seen with striations, ridges and void :-,. Growth ITlorphology lO and electri ca l propert ics I I of the crys ta Is grown hy above methods were stud ied. These properties were influenced by the presence or grav it/~ and so lfdifica ti on or InSb from the melt I '. Further, undoped and doped crystal s showed mobility 6 x I O.l cm2/Vs and7 x 10 \ cm2/Vs respectively at 30() K. In the growth process heat transfer coeffi-
. 1.1 t' f"I I " d' f III clent , urnace temperature pro I e ' an Inter ace play major roles. We have mod ified the VDS technique and growth parameters were optimized for high degree
of crystallinity of InSb, InGaSb, InTeSb. GaAISb and GalnSb. In the present investigation. we report the growth of InSb and InTeSb crystals by VDS technique.
2 Experimental Procedure Growth of undoped and Te-doped InSb crysta ls has
been performed using VDS techniques . Detailed experi mental procedure is ex plained else.w here l 7 Thl' 1ll,Iin features of the growth are briefly given here. Indium and antimony in stoichiomet ri c proportion were kept in quartz tube conical at one end . Doped crystals were grown by mixing Te into In and Sb charge before sealing. The quartz ampoule with charge was evacuated ( 10-<; torr) and back fi lied alternately lOti meso then ampoules were sealed by refilling of argon (350 torr) . A typical growth cyclogram is shown in Pig. I (a). The growth of InSb crystals were performed by lowering ampoule from the hot zone at the rate of ~ mm/hr ,1I1e1 rotational speed at 10 rpm .
The ingots were slieed perpendicular to the growt h
ax is of thickness son ~lm . Suhstrates were lapped hy carborundum power and poli shed by alumina abrasive. The ohmic contacts using indium were made at fo ur corners of the substrates for Hall measurement. The substrates have also been used for the fabrication of P-II junction di ode, Schottky di ode and MOS dev ices .
INDIA ' .1 PURE & APPL PHYS. VOL ]X, APRI L :W()()
In thi s paper, we report the growth morphology observed through Nomarsk i optical microscope. Phili ps X' pert single crystal di ffrac tometer has been used for the single crystal ~1I1 ~ d vs i s. Resisti vitv was measured
using four poin t probe set up and Hall vo ltage l1leasurements were made using fo ur probe CTI c losed cyc le liquid He-cryostat and magnetic fi e ld set up at 2.7':. kG .
800
700
600
U 500 0
w 400 a::: :J r-<I: 3 00 a::: w 0... 200 2 w r-
100
800' C CRYSTAL GROWTH PROFI LE
Lower ing rot.
10mm/ hr Rolot ion rol.
10 rpm
575'
In Sb - 16
. lI[ 530 liquid - Sol id - - ---- - 17 bou ndorv
:nz:: Crystal Growth
>f-
8
Lower ing rol e 3 mm / hr
Rotol ion ro le
10 rpm
16 1
24 32
250'C
3ZI
40 48 56 64
GROWTH TIM E ( hI's)
ORIE NTATrON PATTERN
(X'pert Philips Diffractom~ter) PollnSb 135/0 Omeoo 16 .980
(22 0) 2The,o 3 9 .2 5 8 Phi 14.0 0 0
P.1 7.350 XO.OO
YO.OO
10000
8750
7 5 00
InSbP5-4(growth no.J6)
FWHM : 72 arc sec
Mobility: (T c 300 K)
fL : 5 ·7x I04cm2/ V.Sec.
6250
(j) 5000
Z
~ 3750
Z 2 500
125 0
°1~6.4;:7;;;5-~---:-:-!~-~--'-_...J 17.485
OMEGA / 2THETA(deQ)
\
'.,W \ \ \
-.L.J 72 80
Fig. 1- (; ,) Optim ized t!rCJwth cyc logram ane! the crysta l growth process usee! in growth no. 16 ane! (b) X-ray di f fraction pallerns for (22()) rclkc l ion shows the si ngle phase growth wi thout seed i .e. sel f-seeded growth and FWHM 72 arc sec
GADKARI & ARORA: CHARACTERIZATION OF InSh CRYSTALS GROWN BY VDS TECHNIQUE 2)1)
3 Results and Discussion
3.1 (;rowth morphology
3. 1.1 As grown crrswls
A ll the ingots came out of ampoule very eas ily afte r gentl y tapping and the surfaces had a dull appearance
but the conical regions of ingots were more shiny and smooth . There was no sign of stri at io ns, voids and ridges
on the ingots grown by the optimi zed growth conditions.
Ingots in thi s growth showed contraction in diameter,
which revea ls that the me lt was not sti cking to the wa ll
and the di amete r of the ingots are sma lle r than the in te rna l d iamete r of the quart z ampoule. The ampoules had suffi c ient space above the melt. The refore, verti ca l
stress on solid ifying crys ta ls would be absent. The dewetti ng was observed simil ar to that in Ref. 6 . Contracti on in the di amete r revea ls the absence of contact between in got and ampoule wall durin g solidificati on, whi ch red uce the radi a l heat fl ow . The refore, the te m
pe ratu re grad ient was maintai ned steady a t c rysta l- liquid in te rface. Furthe r, it reduces the rmal stress o f the
ampoule on the in got surface. T hi s re vea ls the conditio n of three phase bounda ry (TPB) i.e. the me lt-crystal-ampoul e wa ll was criti ca ll y sati sf ied in VDS technique.
Th is results in the growth of nea rl y pe rfect s ingle c rys
ta ls of JnSb. The rotati on of ampoules ass isted in averagin g out the temperature asy mmetries. Furthe r coni cal
angle less that 20° promoted sing le nucleati on w ith steady liquid -solid inte lt·ace. The ine rt argon pressure
ins ide the ampoul e prevented Sb loss . Quartz tu be growth chamber with a ir channe l he lped in stabili s ing
li quid-crystal inte rface shape (pl ane or convex) near the
melt. The refore, the rmal st ress was curbed and radia ll y outer pa rt was last freezin g reg ion in that layer. Apparentl y. it has resulted in the no sti cking of me lt to wa ll s
of the am poul es and no e ntrapping of bubbles. The sing le crysta l growth could be possibl e by these opti mi zed growth conditi ons in V DS technique.
.1. 1.2 X-mr rl i/fi '{/ l'I io/l
FWHM of X-ray patte rn of (220) re tl ee tion for a good qua l ity InSb ingot no . 16 was o.m degree as compared
to 0 .3° for low quality ingot no . 8. The powder patte rn of diffrac ti on peaks is in agreement w ith star marked AST M data and JC PDS card no. 6-20S. S ing le c rysta l growth was confirmed a lso by Philips X ' pe rt diffracto meter w ith FWHM 72 arc sec. Thi s reveals that se lfori entat ion growth wi thout seed is possible by thi s tech
niq ue. see Fig . I(b). The Laue d iffraction pho tograph a lso revea led the sing le c rystal nature of the undoped and Te-doped [nSb c rysta ls .
3.1.3 Ulldoped growth
Poli shed substrates of und oped growth were etched
in CP4 and modified CP4 (HNO,: HF:C H1COO H:H20 : :5:3:3: 10 for 7-1 0 s) . Etched samples revealed the eu
tecti c mic rostructure as shown in Fi g. 2(a). These fea
tures re prese nt g row th o f two so lid ph as es o f
decomposition in homogeneous layer as probed by
EDAX. Sb-rich regions are non-sto ichi ometri c growth
regions with decorati ve mi crostructures and the ex
tended regions of it reduced the ir s ize away from the
ma in eutectic regions. These are the vo lu me de fect
regions formed by constituti ona l supercooling and mi
crophotograph ex hibits the eutect ic embedded fea tures.
Undoped growth showed conical etch pits (EPD 2 x 10"
c m2) revealing the c lu sters of point defects and site of
di slocation. Further, undoped low qua lity c rysta l growt h
is seen with intrinsic crysta ll ographic (twin boundary
and gra in boundary) microstructures . By the optimized
growth condition, the eutec ti c mic rostructures and ex
tended defects are e liminated .
3.1.4 Te-doped gm wth
Etching procedure is s imilar to the undoped growt h.
Heav il y Te-doped growth showed stacking fau,l ts ancl
striations. The magnified version of band formati on is
shown in Fig. 2(b). Interestingly, the eutecti c micro
structure and conical etch pits are absent in thi s growth .
Heavil y Te-doped growth reveals that the fo rmer mi cro
structures are restri cted but resulted in impurity band
formation. However, the heavi Iy Te-doped growth was
a lso seen with Te-precipitate and micro-c racks. T hese
features (heav il y) reveal that the doping concent rati on
( I Olt) cm' ) varied significantl y in ingot and resulted into
compos itional stresses in the form of microstructures .
Excess Te may be precipitated due to non-availability
of space to occupy within the In-Te-Sb structure. Pre
c ipitates were observed in heavily Te-doped ( 1.7 x IOlt)
cm-~ ) ingots but absent in li ghtl y Te-doped (5 .2 x 10 17
cm-~ ) growth . The high degree of c rysta ll inity growth o r
undoped and Te-doped In Sb c rysta ls resulted into lik e
mi crostructures, such as low angled crys ta ll ograph ic
defec ts and conical e tch pits. The c rysta l in g rowth no .
16 (see Fig. I) had drasti c reductio n in mi c rostructures.
However, eutectic microstruc tures were dependent on
the ampoule lowing ve loc ity and vertical pos iti on. T hi s
indicates that if the ampo ule lowering ve loc ity becomes
equa l to the eutecti c growth rate then the decompositi on
in the melt is favoured at hi gh temperature .
INDIAN J PURE & APPL PI-IYS, VOL 38, APRIL 2000
J.2 Electrka l properties
3. ~ . I 111Ir/o/!('r/ CITSI(fls
The Hall-Van cle f' Pauw measurements have been made ill T = ~()() K. The H;d I measurements at 20 K of these inlloh are show n i ll Tabl e I. The low quality ingol
showed hi gh impurity concentrati on ( 1.6 x 10 17 cm- \
low mobi lity (4 x to; cm2/Vs ) and the variation in concentration along the ingots. This reveals that there are different Iypes of impurity. Growth no 16 showed
hi gher mobility (5 .6 x 10-1 cm2/Vs) for optimized growth conditi ons with improvement in crystallinity. The carri er concentration (2.4 x 101
(, cm-I ) is slight ly hi gher
than the intrinsic carrier concentrati on (2 x 10 1
(, cm-') at
'Ioo~m .
Fi),! . 1 - 1:1) The eutectic micl'(lstrll clurc phl)\u),! raph and
(h) ilc: l l' il y Te-doped sa 111ples arlO seen with h:11ld rormation and
stack in ),! 1':11111
Tahle I - Hall measuremenl or undoped and T e-dopecl samples
al 20 K
Crystal M()~ ili t y Resisti vity Carri c: r H:tl i cm-/V s ohm- e111 Densit y cperl , "
NI-I l'IIl 'leu\. em
InShpl - 7 524 O. I X () .6:1 x I OIr' 1) 5
InShp2-4 ~40() 0.14 1.:11 )( I OIr. 47()
InShp2- 12 977 0. 15 4_0X x 10 1(, 154
InSh1l2-4 28X40 3.7 x IO-l S.X x 10 17 - IOJ)7
InShn2- 12 29000 3. 85 x 10-1 5.19 x 1CP - l UX
T= 300 K. Therefore, mobili ty has be n decreased with decrease in concentrati on of carri er~ 1 see Fig. J( h) I, a;.
. II) the compl ex boundary IS closer to the above va lues .
The Hall coeffici ent as a functi on of temperature is represented in Fig. ~(a) . The undoped material s showed net p-type conduction in low telllperature ran ge (e.xtrinsic range) whi Ie cOlllpl ex conduction of carr iers are see n after the inversion temperature up to max imum negat ive va lue of RH. The va lue of RH decreases slowly with increase in temperature, which reveals the degenera te mode of conducti on. In this in vest igat ion the R" Illeasurement has a shift towards hi gh te lllperature side. Similarl y, the RH = () ( inve r.~ion te lllperarure) has bee n observed to the hi gher telll perature :.; ide. These two results are new and con tradicts the existing result. Our results are seen as i Illprovements in crysta II i n ity and hi gher Illob ility of InSb crystals grow n by VDS technique. Below 100 K the salllple InSbP2- 12 showed the illlpurity conduction by increase in RH with decrease in te lllperature but with further decrease in te lllperature RII
is a lso decreased wh ich showed the im purity ioni zati on below ~O K. The result s of carrie r concentrati on versus Illob ility and RH at 300 K is shown in Fig. 3(b) . TIll' transport properties of InSb crys tal s are reported e lsewhere I ~ . It is observed that the InSbP2-4 samples showed hi gher Illobility of holes at 20 K and lower concentration of holes, see Table I. Radi al colllPos itional variation .~
were absent in undoped growth as confirllled by the res istance Illeasurements.
3.2.2 TI' -doIWd (' rrs/III.I·
The substrate fo r Hall Illeasurelllents had bee n prepared by the procedure laid down for the undoped wafers and the Hallllleasurements are shown in Fig. 3( b) . The impurity distributi on al ong the growth axis showed un iform distributi on of sin gle irnpurity. There is no large
GADKAR I & ARORA CHA RACTERIZATION OF InSh CRYSTALS GROWN BY YDS TECHN IQU E 24 1
variation of Hall measurements along the length of the ingots; which revea ls that the growth conditions resulted
. in high degree of crystall inity of the doped materi al. The elect rica l characteristics of the Te-doped InSb crysta ls at T= 20 K are represented in Table I . These properties are seen uniforml y di stributed at low temperature. The measurements were taken 0 11 two samples which were obta ined from the different sections of the ingot. Hall measurements on undoped and Te doped samples are in agreement with Ref. 19. The uniform distribution of impu rity in undoped and Te-doped inSb crystals al'e re lated to the rotation of the ampoule. in the BridgemanStock barger method there is no relati ve motion of the crys tals and ampoule. The rotation mi ght h<lve assi sted
1000
.D
E o ;:l o 100 u '-
r<J
E u
I 0:
~, o \ • I
o . \ \ I \ I
in stirring the melt as we ll as uniform radial temper<ltu re during solidi ficat ion of melt. This effect will maintain the shape of liquid-solid interface steady throughout the crystal growth. The resist ivity measurements reveallhc uniformity in compositi on ax i<l ll y as wel l as radiall y in Te-doped growth.
4 Conclusions The main aim of the modificat ion in the VDS tec h
nique is to develop a method for growth of bulk crystals. The experimental results showed that by the VDS technique good quality InSb crystals could be grown reli ably. The propert ies of InSb crystal s were confirmed by the X-ray , Hall, Four point probe measurement s ancl chemi ca l etching. The VDS technique has been pro-
., I'
2
1. In Sb PI -7
3
2 . In Sb P2-4 3 . InSbP2-12
1 0 ~ __ ~ ____ -L ____ ~ ____ ~ __ ~ ____ ~~~~ __
3 4 5 6 7 8 9 10
1000 k-I T
106
10 3 102
( b ) Mobilit y :; o p- ln Sb e • n-lnSb
",'-E
u Hall coeff u
Q)
105 r-
(f) • p -InSb Id 10' .Ll
Z > .0 CJ) W
"- CJ) ~ S! N
E oS Ii. '" Ii. U
'" ~ w >-
a. - 0 4
,., c u
f- lO Id ~ I -' ..J -' iIi « 0 :r: :2'
103
I 0 . 1 10'6 1020
CARRIER CONCENTRATION (cm3)
Fig. :1 - (a) The gr;lph oi" HH versus tcmpcraturc givcs the I?hlllax. HH = () ( invers ion temperature). which arE' shi fl ccltllwa rds the hi !.!hcr side ni"thc tempcJ"<lIurc i"or the high quality crysta ls. This is in conlrast with ex isting result . T he graph represcl1l s (h) thc c 1ITicr '
CllllCcnlration again st the mohility and Hall coelTic ient (HH ) for the undoped growth (!'- type) and Te-doped ( /1- type) lnSh crystal s ;It :100 I,
242 INDI AN J PURE & APPL PHYS. VOL 38, APRIL 2000
posed for the growth of e leme nta l and mixed compound semiconductors.
Acknowledgement The authors would like to express thanks to Dr A J
S ingh (C hemi stry Department , BARC, Mumbai) and
Prof K S C handrasekar (UGC Emeritus), fordi scuss io ns
and va luable suggesti ons. Thanks are a lso expressed to Prof S B Pate l. (Head), Department of Physics, Univer·
sity of Mumbai fo r the fac ility extended durin g the
crysta l growth . One of the authors (DBG) would like to
thank the Principal. Mithiba i College, Mumbai .
References I Wang P Y . Chem J F & Chen W W . ./ Crr .1'! Crowlh. 160 ( 1996)
24 1-49.
:: Chen L P. Lou J .I . Li u T N. Pang Y M & Yang J S . ./ Solie!
S it l/t · U{'{' I/Wl . 35 ( 1992) l OX I .
.\ Thoma, R N. Hohgoud H M. Ra vishankar P S & Briggins T T. Prog Crysl Cro wlh & C/Il/me l Mm ('/' . 20 ( 1993) 219-253 .
4 Partin D L. Green L & Heremems J. J Eleclron Masler. 23 ( 1994) 35-79.
5 Lin M H & Kou S . ./ Cn'SI CrolVlh. 152 ( 1995) 256-60.
Duffer T . Paret I & Dusserre P . ./ Crr sl Crowlh . 100 ( 1990) 171 - I X4.
7 Derebai l R, Wilcox W R & Regel L L.'/ Crvsl Crowlh . 11 9 ( 1992) 98-110.
8 Pfeiffer M & Munlbrig M . ./ C rvst C rowth . 11 8 ( 1992) 269.
9 Ostrogorsky A G. Sell H J. Schar! S & M ulcr G . ./ Cn 'sl Cro wth . 128 (1993) 201 : 137 ( 11)94) M .
10 Rosenberger F. Prog Crrst Cro wth & C/w /'{/ ct Mil t{'/" . 2(>
( 1993) 87- 9X
II Holmes D E & Koo L Y. Maler Res Bu ll . 30 ( 1995) 453-6 1.
12 Derebail R. Wilcox W R & Regel L L. .I Space Rockc/.l'. 30
( 1993) 202-207.
13 Meyer S & Ostrogorsky A G . .1 Cryst Crowth . 17 1 ( 1997) 566-76.
14 Banan M . Gray R J & Wilcox W R . .1 C ryst Crowth. I 13 ( 1991 ) 557- 565.
15 Neugerhager G T & W ilcox W R. A ell/ A.I'/rol1l1U1im. 25 ( 11)(!1 )
357- 362.
16 Kuppuran S & Derhy .l J . .f ('n 'sl Crowlh. 172 ( 1()<) 7) 351)-360 .
17 Gadkari D B. Lal K B & Arora B M . Bull Ma ler Sc i. 2 1 ( 11)9X) 127-1 31.
18 Gadkari D B. Lal K B. Shah A P & Arora B M . .1 Crvst Cro wth .
173 ( 1997) 585-88.
19 Y ang Y J. Park M K . Tee S I (' t a l .. .1 A fJp l Pin's. 69 ( 199 1) 3109.