Recent progress in characterization of III–V compound semiconductors

Prog. Crystal Growth and Charact. 1985,Vol. 11, pp. 291-298

O146-3535/85$0.00 + .50 Copyright~) 1986PergamonJournalsLtd.

Printed in Great Britain. All rights reserved

RECENT PROGRESS IN CHARACTERIZATION OF lll-V COMPOUND SEMICONDUCTORS Q. H. H u a , Y. Z. S u n , S. R. X u e a n d G. P. Li Tianjin Electronic Materials Research Institute, Tianiin, China

Introduction

Crystal

growth of III-V compound semiconductors in China was in its infancy in the

fifties, since then very rapid progress has been made to produce materials for various applications.

This work has been rewarded by the achievement of many new microwave and

photoelectron devices.

A new problem has accompanied the development of these materials

however, namely, the necessity of evaluating the materials with respect to their purity and crystalline perfection as well as electric parameters.

Numerous analytical methods have been

developed in many laboratories, including measuring the amount of foreign elements in the highest purity materials, or directly observing crystalline imperfections.

This paper reviews the recent progress of methods available in the characterization of I I I - V compound semiconductors, both at our Institute and elsewhere in China.

it certainly cannot cover all the aspects of this field.

Nevertheless,

Techniques will be basically

confined to the electrical, structural and chemical analysis, along with some examples.

1.

Electrical

It is well known that the Hall bar or Van der pauw method has been regarded as one of the standard measuring methods used for semiconductors, from which the free-carrier concentration and mobility are obtained.

By means of the dependence of carrLer concentration

on the reciprocal temperature and the technique of mobility analysis, the compensation of materials is also determined.

Lately, with the development of C-V technique, MES-Hall

measurements are developing and have won great success in the carrier concentration or mobility profiling for sub-micron epitaxial layers.

It was reported that the Hall system had been accomplished with programming data acquisition, but usually it had to feed the data to a separate computer for calculation. (1,2).

According to the situation in our lab, we have designed and constructed full autodata

a@quisition and processing under fixed or varied temperature conditions,

291

The data fitting

292

O H HuaetaL

technique is also available, by utilizing preprogrammlng files stored in materials, e.g., Si, GaAs, InP, etc., can be determined.

All results are output at the periphery.

The traditional method to determine Ei by the Hall method is to simplify the charge neutrality equation under low temperature condition then use a graphic technique.

However,

this technique has faults as it cannot identify the result as Ei or El/2, due to the different measurement temperature range and sample compensation ratio.

In order to avoid

this fault, and furthermore to lower the measurement cost, we have developed a computer-aided technique to process the experimental data taken from 55 to 300K by use of reduced pressure liquid nitrogen instead of liquid helium.

The only prerequisite is that the dependence of

carrier concentration on the reciprocal temperature must have obvious deionization. addition, the ratio of effective mass (m*) to degeneration factor (g), (m*)3/2/g, fitted out in the same procedure.

In

is also

This technique has been used to analyse III-V compounds

and Si, and the results are satisfactory and consistent with graphic techniques within a deviation of ± 10%.

But the measuring condition for the latter is rather critical.

For

example, the results for Ge doped P-type GaAs are listed in temperature range from 20 to 400K.

Table i: Activation energies E A of Ge doped P-GaAs obtained by computer-alded analysis

Sample No.

EA(ev)

NA(1017cm -3)

ND(IO16em -3)

DG-I

0.0286

3.73

7.48

DG-2

0.0288

4.40

8.40

DG-3

0.0232

6.52

13.60

(3)

0.031

1.46

2.70

(3)

0.023

5.15

1o.oo

Figure I shows the data of Table I in the form of ig (P(P+ND~)

(i)

(NA-ND-P)

(Nv)

as a function of I/T.

The curves for each sample are straight lines, indicating that this method is feasible for determination of Ei without the low-temperature condition.

The other application of Van der pauw method is to analyse pure materials both of bulk and epilayers, Xu Shouding et al. (4) measured the electric properties of high purity GaAs grown by LPE and VPE technology. the result is shown in Fig. 2.

We have measured the mobility of an undoped InP sample, and The dependence of lattice mobility on temperature at higher

temperature is founded as follows on the basis of Brook-Berrlng formula and Walukiewich's work (5).

L = 9.24 x 108 T-2-16

(cm2/V.S)

(m* = 0.062 mo)

Characterization of Semiconductors 1

I=

293

00

lo -1

v

~1 z

DG -3

1 0 -2

. DG-2

-

DG-I t 5

10-3

I 10

I 15

Fig. 1 The dependence of Ig(P(P+ND~ ) (I_)

I 20

T -1 ( Io -31

on I/T for each sample listed in Table I.

(NA-ND-P) (NV)

/

105

--

/

%~, %

/

--

/

_>

/

/

//\(/ /

//'/

%

"N\ \%

104

3xto 3

Fig. 2

I

I I'llfll

1O0

I

200

I

I I

400

T

The mobilitles function of temperature of a pure InP sample

The deep l e v e l s in undoped s e ~ t - i n s u l a t i n g (SI) GaAswere d e t e c t e d by Zhou B i n g l i n e t a l (6) u s i n g the Hall method a t the temperature range of 180 t o 500K.

They found two kinds of

samples, according to the results, that were the high-resistivity samples with El of 0.71-0.64 eV determined by EL2; and the mld-resistivity samples with Ei of 0.43 ev and 0.37 eV determined by EL5 and EL6, which is slightly different from the report by Martin et al (7).

Photoluminescence

spectra of LEC-InP were investigated at low temperature by Wu Lingxi

et al. (8) , which identified each peak in the spectra in relation to impurities in the sample.

Q. H. Hua et al.

294

2.

Optical method

Conventional evaluations of III-V compounds are by electrical techniques as mentioned above.

However, optical methods have some attractive points.

The study of various kinds of

optical absorption relating to the photon energy not only has practical meaning in the design and engineering of devices, but also provides much interesting information on the energy band structure of materials, such as band gap, effective mass and lattice deformation potential constant.

In addition, this is a non-destructive, contactless method, so the advantage is

obvious in measuring SI materials due to the difficulty of making ohmic contact.

For the doped semiconductors, we have measured the surface free-carrier concentration and mobility by analysing the infrared reflectance spectra of the LEC grown InP using a FT-ZR spectrometer (9).

Two reflectance minima Can be observed in this spectrum as shown in Fig.

3, which is similar to GaAs.

By checking a universal chart presented in our previous paper

(9), the free-carrier concentration and mobility are obtained.

From second minima, the

lowest measurable limit of the carrier concentration can be extended to 7 x [016 cm-3. 9O No. 1. 6O 5O v

O No.3.

6°I

Z 50 ~0

6O 50

740

650

560

470

~30

Wavenumber ~ Fig.3

290

250

110 20

(cm-1)

The two reflectivity minima, for three InP samples, the concentration for each sample are: No l:

7.9 x 1016 cm-3, No 3:

With t h e i n c r e a s i n g

interest

been d e v o t e d t o s t u d y i n g p r o p e r t i e s a l . (10) a t t h e I n s t i t u t e

4.5 x I017 cm-3, No 5:

2.7 x 1018 cm-3

of GaAs IC b a s e d on SI-GaAs, a g r e a t d e a l o f e f f o r t of this material,

has

f o r C r - d o p e d SI-GaAs, Xu Z h e n j i a e t

of S e m i c o n d u c t o r Academia S i n i c a ,

ha ve e s t a b l i s h e d

curve by neutron activation analysis for measuring of Cr content in SI-GaAs.

a caliberation More recently,

we have investigated the carbon contamination in undoped LEC, in situ synthesis SI-GaAs by infrared absorption method, and the spectrometer is operated at the highest resolution of 0.06 cm-I wavenumber and the speciman is cooled down to 1OK wlth a helium compressor.

Under

295

Characterizationof Semicondu~ors these conditions, we observed the fine structure of C absorption band around 582 cm-I, as shown in Fig. 4, where five split peaks are observed.

An explanation for this proposed by

Theis et al.(II) is that the carbon in GaAs is predominately on As site, and forms different vibration models with its nearest neighbour configurations of the two Ga isotopes, Ga 69 and Ga7l.

In fact, as the sample temperature decreases, the carbon absorption coefficient increases, thus, the detection sensitivity of C is improved.

In addition, we have measured

the water content in B203 and EL 2 deep level in Si-GaAs, and the close relation of H20 in B203 to C in GaAs, and EL 2 to the stoichiometry of melt (Ga/As) are found.

Therefore, a

convenient way to study the compensation mechanism in undoped SI-GaAs is established.

~O

,oo

583~.25

582.5o

I

581.75

581.00

Wavenumbers Fig. 4

The fine structure of C absorption band under 10K and 0.06 cm-I resolution

3. Structural

Defect studies of semiconductor crystal in early days normally used chemical etching and optical microscopes to detect the dislocation density and its distribution.

Defect formation

and elimination mechanism with crystal growth conditions such as dopants, thermal field, seed, etc. are also studied to seek a low defect growth technology.

Recently, more critical

qualities of wafers are desired by the manufacturers of devices and circuits, therefore, X-ray topography and high voltage electron microscopy (HVEM) are used to investigate microdefects, microprecipitation in crystal and interracial defects exsisting in epilayers. He Rongjia et al. (12) have observed microdefects and microprecipltations in Te or Si doped GaAs grown by the horizontal Brldgman method, using chemical, anodic etching and TEM technique.

They find these microdefects and their features are dependent on the carrier

concentration of samplest and most are the extrinsic faults and Frank loops with

296

O.H. HuaetaL

precipitations.

They have also noticed that the hillock or S-shape pits revealed by etching

c o r r e s p o n d e d t o the c l u s t e r

of t h e s e m i c r o d e f e c t s o b s e r v e d i n TEM. The i n t e r f a c i a l

of LPE-GaA1As/GaAs were i n v e s t i g a t e d u s i n g lO00kV HVEM by Liang Jun Wu e t a l . ( 1 3 ) , have measured t h e d i s t a n c e from d i s l o c a t i o n b r i g h t f i e l d and weak beam t e c h n i q u e s .

network t o t h e i n t e r f a c e

Defect c h a r a c t e r i z a t i o n s

p u l l i n g procedure. (see Fig. 5).

shapes respectively,

s u r r o u n d e d by d i s l o c a t i o n s

generated during the

Two t y p e s o f complex d i s l o c a t i o n

c l u s t e r s a r e a l s o o b s e r v e d , and t h e c e n t r a l c o r e of t h e s e c l u s t e r s triangular

by means of h i g h o r d e r

of LEC-InP have been s t u d i e d

by TF~ i n our l a b ( 1 4 ) , and we have o b s e r v e d some s l i p d i s l o c a t i o n s cooling process of crystal

defects and they

cellular

a r e s p h e r i c a l and and t a n g l e as shown i n

Fig. 5. Rectangular dislocation loops in InP are occurred sometimes, and have clear displacement fringes.

Diffraction contrast analysis indicates that they are the extrinsic

stacking fault with Burger's vector of b = (I/n)[110] (see Fig 6),

In the Isoelectronic

doping InP ingot, low defect crystals have been grown and some local dislocatlon-free regions are o b s e r v e d .

Fig. 5 Electron micrograph of sllp

Fig. 6 Electron mlcrograph of

dislocation and a spherical core

stacking faults.

surrounding by dislocatlon tangle.

direction is (III) and the

The beam direction is (III) and the

diffraction

The beam

v e c t o r i s (220)

diffraction vector is (220) 4.

Surface From t h e l a s t decade,

increasing attention,

t h e s u r f a c e and i n t e r f a c e

Many l a b o r a t o r i e s

s t u d i e s of I I I - V compounds have r e c e i v e d

i n China have been e q u i p p e d w i t h advanced s u r f a c e

a n a l y s i s i n s t r u W e n t s s u c h a s XPS, UPS, AES and SIMS.

Among them, Fudan U n i v e r s i t y i n Sanghai

has a l a r g e g r o u p , l e a d i n g by P r o f e s s o r Xie Xide w o r k i n g on s u r f a c e p h y s i c s and o t h e r projects,

t h e major r e s e a r c h a c t i v i t i e s

a r e c o n c e n t r a t e d on s u r f a c e r e c o n s t r u c t i o n ,

297

Chara~erization of Semicondu~om electronic

states

theoretically

and c h e m t e o r p t i o n on s u r f a c e o f m e t a l s and e e a i c o n d u c t o r s , e t c . ,

and e x p e r i m e n t a l l y .

P h y s i c s and I n s t i t u t e surface analysis

Other w e l l - o r g a n i z e d l a b o r a t o r i e s

both

are at the I n s t i t u t e

o f S e m i c o n d u c t o r s , Academia S i n i c a i n B e i J i n g .

I n our I n s t i t u t e ,

of the

l a b i s b e i n g expanded.

Suaaary Some e v a l u a t i o n methods, based on H a l l measurement, i n f r a r e d a b s o r p t i o n and r e f l e c t i o n and T ~

technique are introduced,

progress in characterization many i n t e r e s t i n g

Although we a t t e m p t t o g i v e a b r i e f

o v e r v i e w o f the

of I I I - V compounds i n China, we r e g r e t b e i n g u n a b l e t o c o v e r

r e s e a r c h work i n t h i s s h o r t p a p e r .

Acknowledgement The a u t h o r s a r e p a r t i c u l a r l y

i n d e b t e d t o P r o f e s s o r B.Z. Song f o r h i s encouragement and

r e v i e w o f t h e m a n u s c r i p t ; s p e c i a l t h a n k s t o Dr H.L. Tu f o r h i s e d i t o r i a l

assistance.

References 1.

H. F u j t s a d a , T r a n . IECE, J a p . , 62, 822 (1979)

2.

K.E. Singer, H.D. Mckell, Iut J Eletr Eng Educ (GB) 19, 307 (1982)

3.

F.P. Rosztoczy, F. Ermants, I. Hayashl and B. Schwartz, J. AppI. Phys., 41, 264 (1970)

4.

S.D. Zu and r.¥. LI, Chinese J. Semiconductors, ~, 389 (1983)

5.

W. Waluklwich et al. J. Appl. Phys. 51, 2659 (1980)

6.

B.L. Zhou and Z.X. Chen, Chinese J. Semiconductors, ~, I00 (1985)

7.

G.M. Martin, Appl. Phys. Left., 39, 747 (1981)

8.

L.X. Wu, X.L. Liu, S.Z. Ye, Q.R. Meng, Y.K. Li, Chinese J Semiconductors, ~, 132 (1984)

9.

Q.H. Hua, G.P. Li, X.K. He and Q. wang, Mater. Left., ~, 93 (1985)

I0. Z.J. Xu, Z.H. Zhang, B.K. Sun, Chinese J Semiconductors, ~, 191 91983)

11. N.M. Theis, K.K. BuJaJ, C.W. Litton and W.G. Spitzer, Appl. Phys. Left., 41, 70 (1982) 12. H.J. He, F.I. Cao, T.W. Pan, Y.K. Bai, X.Y. Fei and F.L. Wan, Chinese J Semiconductors ~ , 7 (1981)

13. J.W. Liang, Z.W. Shi, Q.Y. Ren and J.L. Ju, J. Chinese Electron Microscopy Soc, ~, II (1984) 14. S . g . Xue, L Q . Wan, C. Li and X.L. Chen, i b i d . ~ , 58 (1984)

298

O. H. Hua et aL

THE AUTHORS

Q. H. HUA

Q.H. Rua was born in

Y.Z. SUN

1936 in China.

Physics, Fudan University, Shanghai.

S.R. XUE

G.P. LI

From 1954 t o 1958 he was educated at Department of

Following graduation he joined the Hebei Semiconductor

Research Institute from 1961 and Sichuan Solid State Circuits Research semiconductors.

After

joining Tianjln Electronic Materials Research institute in 1979, his major interest turned to characterization of materials.

From 1981 to 1983, he worked on Germanium Nitride and other

thin insulator films at the Dept. of Electrical Engineering of Columbia University as a visiting scholar, where in collaboration with Prof Edward S. Yang.

Now he is senior engineer

of TEMRI.

¥.Z. Sun, born in 1938, graduated from Radio Electronic Department of Tsinghua University in 1962. He has worked in crystal growth research of Si by CZ, and measurement research and characterization analysis of semiconductor materials.

At present he is an

engineer in Tianjln Electronic Materials Research Institute.

S.R. Xue, born in 1937, graduated from the Physics Department of BeiJing University in 1962.

He has worked in crystal growth research of Si by FZ, GaAs by MOCVD, and the

measurement research of semiconductor crystals.

At present he is an engineer in Tianjin

Electronic Materials Research Institute, working on the electron microscopy analysis of semiconductor materials.

G.P. L i , born i n 1939, g r a d u a t e d from t h e P h y s i c s D e p a r t m e n t of N a nka i U n i v e r s i t y i n 1964.

Re h a s worked i n s i l i c o n

epitaxial

g r o w t h and m e a s u r e m e n t r e s e a r c h of s e m i c o n d u c t o r

crystals. At present he is an engineer in Tianjin Electronic Materials Research Institute, working on the infrared spectrum analysis of semiconductor materials.