TRANSPORT PROPERTIES OF AMORPHOUS FILMS OF CADMIUM ARSENIDE

HAL Id: jpa-00220865

https://hal.archives-ouvertes.fr/jpa-00220865

Submitted on 1 Jan 1981

HAL is a multi-disciplinary open access archive for the deposit and dissemination of sci- entific research documents, whether they are pub- lished or not. The documents may come from teaching and research institutions in France or abroad, or from public or private research centers.

L’archive ouverte pluridisciplinaire HAL, est destinée au dépôt et à la diffusion de documents scientifiques de niveau recherche, publiés ou non, émanant des établissements d’enseignement et de recherche français ou étrangers, des laboratoires publics ou privés.

TRANSPORT PROPERTIES OF AMORPHOUS FILMS OF CADMIUM ARSENIDE

L. Żdanowicz, W. Żdanowicz, Cz. Weclewicz, J. Portal

To cite this version:

L. Żdanowicz, W. Żdanowicz, Cz. Weclewicz, J. Portal. TRANSPORT PROPERTIES OF AMOR- PHOUS FILMS OF CADMIUM ARSENIDE. Journal de Physique Colloques, 1981, 42 (C4), pp.C5- 1069-C5-1072. �10.1051/jphyscol:19814234�. �jpa-00220865�

JOURNAL DE PHYSIQUE

CoZZoque C4, suppldment au nOZO, Tome 42, octobre 1981 page C4-1069

TRANSPORT PROPERTIES OF AMORPHOUS FILMS OF CADMIUM ARSENIDE

L. idanowicz, W. idanowicz, Cz. Wgclewicz and J.C. Portal

*

I n s t i t u t e of Solid State Physics PAS, Zabrze, Poland

"

Amorphous films of Cd3As2 have been vacuum deposited at Ts < 400 K. Halo-type diffraction pattern and microstructure composed of sphero-like clusters cha- racterize the films. Some excess of arsenic was revealed by X-ray microprobe anslysis. Two groups of a-films were found : /A/ high-ohmic films with P ^%

I O - ~ - 1.0 0hm.m and WH below 1 0 - ~ m2/v.s and /B/ low-ohmic films with p 'L

10

'

Introduction.- Bulk cadmium arsenide Cd3As2 is always in the crystal-

l i n e f o r m . However,it is possible to obtain thin amorphous films of

CdgAs2 by thermal vacuuru deposition of bulk zaterial onto various substrates held at temperature below about 400 I< b,23. The obtained a-films have been characterized by smeared halo-type diffraction pattern and by microstructure /examined in electron microscope by trznsmission and replica methods/ conposed of amorphous agglomerates /clusters/ of sphero-like or fibrous shapes with dimensions being depended on the deposition conditiocs l21. Average dimension of the clusters for the films prepared at room temperature is 0.1

-

;&dial distributioc function end local atomic arrangement differ from these for crystalline Cd3As2

141.

This deviation of stoichionetry s e e m to be the reason of filns asorphicity.

Experimental.- Thin a-filns of Cd3AsZ for these experiments mere pro- duced by thermal vacuun: /10-' T o m / deposition of bulk Cd3As2 onto mica or glass sxbstrates held generally at room temperature b-3,5].

Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:19814234

C4- 1070 JOURNAL DE PHYSIQUE

The films had a thickness ranging from 0.5 ,um to 10

p.

The arran~enent for the measurements of electrical and thermoelectric 1,roperties was described in [5J.

The techniques of second differentiationor linear compensation were used to extract the Shubnikov de lTiaas oscillations at strong magnetic fields /ap to 30 Tesla/ and low teuiperatures [6,7].

THble 1. Corzposition and electrical resistivity for a number of a-films of Cd3As2.

Sanple at.% Resistivity

no. cd AS ohm. m

a-145 a-1 43 a-1 49 a-147 a-144 a-39 a-X20 a-K5

bulk

50.5 high-ohmic 50.4

50.1 46.8 45.3

44.1 Group B

40.9

38.3 2.54~10

40 l

o - ~

2esults and discussion.- Cn the base of the conductivity, Hall mobi- lity and thermoelectric power ~easurenents the two groups of anorp- hous films can be resolved:

/A/ high-ohmic f i l m of resistivity I O - ~ to 10" ohrn.m, low Rall mo- bility pz from IO-* to I O - ~ n2/v.s and thermopower S of -100 to -533 /uV/ciag deposed with rate in excess of l00 g/s with considerable non-stoichionetry, see Table 1 and

/B/ slowly deposed low-ohmic f F l ~ s of better stoichiometry with f'cl~-~ ohe.n, pl, = /2-5/~10-~ z2/v.s and S of -60 to -100 pV/deg, The typical temperatare dependeoces for the representative films of

both groups are shown in Pig.1,

The calculate6 values of activation energies changed from sample to s a ~ p l e and were in the range b Z g = 0.20

+

+

eV, /optical energy g a p E

r0.4

For discussion of transport mechanism in these films the biott8s-CFO model in connection with heterogeneous chaotic band model f9] due to disorder and granular structure of the film seem to be applicable.

In this node1 the electronic states at the band extremities are loca- lized in the Anderson sense. ?or the films of group B the strong electron concentration and very high electron mobility and its non- activated character at low temperatures suggest that the conduction is

due to a degenerate electron distribution in non-localized states

Pig.1. Temperature dependences of c o n d u c t i- v i t y C?, H a l l m o b i l i t y p a n d t h s m o - power S f o r two t y p i c a l ! 8 e p r e s e n t a t i - ve samples of group A /sample no,18/

and grou? B /sample 110.56

/.

above t h e c r i t i c a l e n e r - gy 2 i n t h e a l l teope-

C

r a t u r e r a n g e w h i l e i n t h e f i l n s of group A t h e t h e r m a l l y a c t i v a t e d c o n d u c t i v i t y a n d s u c h lower m o b i l i t y s u g g e s t t r a n s p o r t p r o c e s s t h r o u g h l o c a l i z e d sta- t e s below Zc a t l o n t e i n p e r a t u r e s .

For t h e low-ohnic ; i l m s of z r o u p B a l s o a veL1- d e f i n e d s e r i e s of Shu- bnikov d e IIans oscillc?,- t i o n s h a s been a p p e ~ r e d a t h e l i u m t e m p e r a t u r e s and f o r magnetic f i e l d s

>10 T e s l a , Fig.2.

These o s c i l l a t i o n s are q u i t e comparable w i t h t h o s e observed i n aono- c r y s t a l l i n e s a ~ p l e s o r p o l y c r y s t a l l i n e f i l m s i n which C a l l m o b i l i t y i s one t o two o r d e r s of magnitude h i g h e r

p,q -

The c y c l o t r o n e f f e - c t i v e mass c a l c u l a t e d from SdN d a t a h a s a n a v e r a g e v a l u e :m d 1 . 1 ~

0

a n d i s e x a c t l y i s o t r o p i c u n l i k e t h a n t h a t f o r c r y s t a l l i n e m a t e r i a l f o r which t h i s v a l u e i s n e a r l y t h r e e t i n e s lower. From t h e p e r i o d i - c i t y of t h e o s c i l l a t i o n s a l s o e l e c t r o n c o n c e n t r a t i o n n S d i ~ 6 x i 0 D 4 m-3 w a s c a l c u l a t e d which i s h i g h e r t h a n t h a t o b t a i n e d from t h e H a l l da- t a a t 4.2 K.

Using t h e c l a s s i c a l r e l a t i o n f o r t h e a m p l i t u d e s o f t h e o s ~ i l l a t i o n s

where Pn i s t h e o s c i l l a t i o n p e r i o d

JOURNAL DE PHYSIQUE

Lt was possible to estimate also so- called cyclotron :nobility p c , which rzpidly increased at E ? 10 Tesla.

This fact in connection with granu- lar structure of the film and high cyclotron concentration nay explain the existence of the oscillations in these a-films. Above 10 T the cy- clotron radii become small compared with the average grain dianeter and the existence of Landau states of very small width in less perturbed inside of the clusters appears po- ssible. Por B = 10 T and n = 12 the radius of the cyclotron orbit is H450

2.

il.q illis sug~ests that the exact crys-

talline order is not essentiaZ for sharp Landau quent ization.

Fig.2. SdH oscillations for a thin amorphous filu of Cd As ; the second deriv2tiGes of the Hall

voltage and the trans- verse magnetoresistan- ce at 4.2 K and 20 15

are shown.

X e f erences.

1. L.Zdano~vicz and S.B3otkowska TSP,

2

2, J,Jurusik and ~ . ~ d a n o w i c z TSP,

67

3. Cz,Wqclemicz, L, Ldnnos?icz an& 3 . Jurusik: Proc.1st Intern.Symp.

on Physics and Chemistry of 11-V Compounds, l:ogilany, Poland Sept.80, ed.?:. J. Gefteri-L. Xancr&cz, p.125

4. A,Burian and J.Auleytner, as in ref.3, p.119

5, Cz,:"jcle~ca and L.Zdanowicz, Proc. Intern. Conf. "Axorphous Semicozd.-78", Pardubice, 1978,p.340

6, L-Zdanowicz and ~,l~wiecien, Vacuum,

27

7. J.C.Porta1, P.!liallace, B.Zdanowicz and L.Zdanowicz, Proc.Intern.

Semicond.$onf., Kyoto, J.Phys.Soc. Japan, 49 /1980/ 1167 8. W. Zdanowicz, L, idanornice, J. C,Portal, S.ksIcenazy, k:.A,Xoaty;

TSF, 79, no.2,/1981/

9. .H.Fritzsche, J.Non-Cryst.Sol., 6 ^{/1971/ 49}