ADMITTANCE CHARACTERISTICS OF NARROW GAP Hg1-xCdxTe n-p-n AND p-n-p TRIPLE LAYER STRUCTURES

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ADMITTANCE CHARACTERISTICS OF NARROW GAP Hg1-xCdxTe n-p-n AND p-n-p TRIPLE LAYER

STRUCTURES

Lin He, Tang Ding-Yuan

To cite this version:

Lin He, Tang Ding-Yuan. ADMITTANCE CHARACTERISTICS OF NARROW GAP Hg1-xCdxTe n-p-n AND p-n-p TRIPLE LAYER STRUCTURES. Journal de Physique Colloques, 1987, 48 (C5), pp.C5-353-C5-356. �10.1051/jphyscol:1987576�. �jpa-00226780�

Colloque C5, suppl6ment au nOll, Tome 48, novembre 1987

ADMITTANCE CHARACTERISTICS OF NARROW GAP Hg,-,Cd,Te n-p-n AND p-n-p TRIPLE LAYER STRUCTURES

LIN HE and TANG DING-YUAN

Shanghai Institute of Technical Physics, Academia Sinica, Shanghai, China

Ltanomal propri6tQ d'admittance pour HgCdTe de bande gtroite a une structure de triple couches n-p-n (ou p-n-p) a 6t6 6tudi6e.

Ltadmittance pour cette structure de triple couches a 6t6 calculee en utilisant simple modele th6orique. En m$me temps, on a discut6 la possibilite de la fabrication d l u n detecteur infrarouge en

employant cette propri6t6 particuliere.

Abstract

The anomalous admittance properties of the narrow gap H g l - x C d ~ T e n-p-n and p-n-p triple layer structures are reported and investigated.

The admittance for this triple layer structure is calculated by the use of a simplified theoretical model. The possibility of making a new kind of infrared detector by use of these particular properties is also discussed.

1. Introduction

In the last few years there has been considerable interest in the narrow gap HgTe-CdTe superlattice and some other 11-VI compound sem- iconductor superlattices. These materials are very important for making infrared detectors. We have found it possible to make thin layer structures by the ion-implantation technology.

Anomalies were observed when we worked on Phosphorus(P) ion im- planted and Mercury(Hg) or Mercury-Indium(Hg-In) diffused Ha-xCdxTe p-n junctions, which are invalid for the current p-n junction theory.

Phosphorus atoms in Hgl-x CdxTe are acceptors (I), after being annealed the phosphorus implanted N-type Hgl-x CdxTe may form p-on-n junction. But the fact is that the damaged surface layer due to the P-ion implantation has an n-type conductivity.~2] So the phosphorus ion implantation into n-type Hgl-x CdxTe may form n-p-n triple layer structures.

Hg interstitial atoms in p-type Hgl-xCdxTe are donorsCd, the diffusion Hg may form an n-on-p junction. But after being annealied at a certain temperature and Hg pressure, a p-type layer in n-type surface will be observed. Therfore, the Hg diffusion into p-type Hgl-x CdxTe may form a p-n-p triple layer structures.

In experiments, we discovered that there is an apperant abrupt change in capacitance-temperature relation of the P-ion implanted and Hg diffused Kgl-x CdxTe p-n junctions. In this paper, the experimental results are shown. A theoretical analysis and calcu-ation are carried out by the use of a simplified admittance model of the triple layer structure. We also analyse the possibility of making a new kind of Hg,-x CdxTe thermoelectrical infrared detector making use of the capacitance and coductivity abrupt change properties.

Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:1987576

C5-354 JOURNAL DE PHYSIQUE

2. Experimental methods and results

Fig.1 Conductance-voltage curves for different temperatures for a phosphorus- implanted Hgl-x CdxTe (X-0.275) n -p-n triple structure device.

Fig. 2 Capacitance versus voltage for different temperatures for a X=0.275 Hgl-x CdxTe n -p-n triple structure device.

We used a non-equilibrium capacitance bridge, which consists of an EG&G M5202 High frequency Lock-in Amplifier, for admittance measure- ment. We also used an HP 4275 LRC meter to measure the capacitance for Hgt-x CdxTe triple layer structures. Fig.1 and Fig.2 show the G-V and C-V curves for different temperatures for a phosphorus-implanted Hgl-x CdxTe n-p-n triple structure device, respectively. Fig.3 shows the C-T and G-T relations for the same device. It is interesting that there is an abrupt change in capacitance near 166K. We can also see from Fig. 1 and Fig. 2 that the capacitance and the conductance anoma- lies occur near 170K. The experimental results in Fig. 1 and Fig.2 are measured by an M5202 high frequency amplifier. The results which are

shown in Fig.3 are obtained by an HP 4275LRC meter. The capacitance- voltage characteristics for different frequencies for an Hgl+ C h T e

(X10.2) p-n-p triple structure device are shown in Fig. 4.

3. Theoretical model for the admittance of Hgt-xCdxTe triple layer structures.

Under the condition of a small alternating signal, a semiconductor n-p-n or p-n-p triple layer structure can be simplified to a series of the two p-n junctions. On the basis of the theory of resistance- capacitance networkL4J we obtained the expression for the admittance of the n-p-n (or p-n-pj triple layer structure.

The total conductance for the semiconductor n-p-n ( or p-3-p) t r i ~ l e laver structure is aiven by

The total capacitance for this structure is given by

-

-

1 OCO

Fig.3 Capacitance versus tempera.ture and the conductance versus tem- perature for a X-0.275 Hgl-x CdxTe n -p-n triple structure device.

Fig.4 Capacitance-volta e characteristics for different frequencies for a Hgt-x CdxTe (X.0.27 p-n-p triple structure device.

A - f = l M H Z , X-f =3MHZ, @-f =I

omz.

Where C I and G I are the capacitance and conductance for the first p-n junction, respectively. Ca and Ga are the capacitance and conductance for the second p-n junction, respectively, a w i s the measuring

frequency.

Fig.5 The theoretical calcu-

lation for capacitance versus a o o

temperature on a HgCdTe

(X=0.275) n -p-n triple layer structure, Solid line-taking 1600

account of deep level to band 2 tunneling capacitance. Dotted

;

line-taking no account of

deep level to band tunneling ¹¹⁰⁰ capacitance.

The expression for the capacitance and conductance of the p-n junctions with regard to the effect of deep levels can be seen in Ref.5. The total conductance and the total capacitance for the Ge

C5-356 JOURNAL DE PHYSIQUE

p-n-p t r i p l e l a y e r s t r u c t u r e s a r e c a l c u l a t e d by e q u a t i o n ( 1 ) and ( 2 ) . The t h e o r e t i c a l c a l c u l a t i o n s a r e i n good agreement w i t h t h e e x p e r i - mental r e s u l t s . [SJ

The c a p a c i t a n c e v e r s u s t e m p e r a t u r e f o r a narrow gap Hgl-x CdxTe (X10.275) n -p-n t r i p l e l a y e r s t r u c t u r e a r e c a l c u l a t e d . The r e s u l t s a r e shown i n Fig.5. It can be s e e n from Fig.5 t h a t only i f t a k i n g i n t o account t h e deep l e v e l t o band t u n n e l i n g e f f ectt51 t h e anomalous p r o p e r t i e s of t h e c a p a c i t a n c e occure. The t h e o r e t i c a l r e s u l t s shown i n Fig.5 a r e v e r y s i m i l a r t o t h e experimental r e s u l t s shown i n Pig.3.

These f i n d i n g s l e a d us t o t h e c o n c l u s i o n t h a t t h e abrupt change f o r t h e c a p a c i t a n c e of an HgCdTe n-p-n t r i p l e l a y e r s t r u c t m e r e s u l t s from t h e deep l e v e l t o band e f f e c t of t h e p-n junction.

4. Discussion

The frequency e f f e c t f o r t h e X=0.2 Hgt-xCdxTe p-n-p t r i p l e l a y e r s t r u c t u r e i s i n v e s t i g a t e d and analysed. The experimental r e s u l t s a r e shown i n Fig.4. A s a r e s u l t of t h e o r e t i c a l c a l c u l a t i o n we f i n d out t h a t t h e frequency f o r t h e c a p a c i t a n c e of t h e p-n-p ( o r n-p-n) t r i p l e l a y e r s t r u c t u r e have a n important b e a r i n g on t h e d i f f u s i o n c a p a c i t a n c e and t h e deep l e v e l t o band c a p a c i t a n c e of p-n j u n c t i o n s .

From t h e experiments we can s e e t h a t n e a r t h e c a p a c i t a n c e a b r u p t change r e g i o n of t h e Hgt-x CdrTe n -p-n t r i p l e l a y e r s t r u c t u r e , t h e temperature c o e f f i c i e n t of c o n d u c t i v i t y d* =0.76 and t h a t of capa- c i t a n c e ge =0.24-0.28 a r e one o r d e r l a r g e r t h a n t h o s e of an o r d i n a r y t h e r m i s t e r w i t h a ~ = 0 . 0 4 . On t h e b a s i s of t h e s e p a r t i c u l a r c h a r a c t e r - i s t i c s we have designed a new kind of i n f r a r e d d e t e c t o r . The calcu- l a t i o n s shown t h a t t h e d e t e c t i v i t y of t h i s new kind of t h e m o e l e c t r i c a l i n f r a r e d d e t e c t o r w i l l be one o r d e r ' s l a r g e r t h a n t h o s e of t h e g e n e r a l t h e r m i s t o r . Changing t h e composition X of Hgl-xCd~Te, we can o b t a i n t h i s kind of d e t e c t o r , which could o p e r a t e a t room temperatures. We have a l s o observed some i n t e r e s t i n g phenomena r e l a t e d t o t h e o p t i c a l response of t n e Hg,-% CdxTe p-n-p t r i p l e l a y e r s t r u c t u r e .

References

( 1 ) R.K. Willardson, Semiconductors and semimetals, Vol. 1 8 , Mercury

Cadmium T e l l u r i d e , Academic P r e s s , 1981.

( 2 ) S. M a r g a l i t e t a l l , J. Appl. Phys. 5 0 ( 1 0 ) , 1979, p6386.

( 3 ) Narrow-Gap Semiconductors, S p r i n g e r T r a c t s i n Modern P h y s i c s , Vol. 98, 1983.

( 4 ) W i l l i a m I. ORR, Radio Handbook, 22nd, Howard W. Sama&CO., I n c , 1981.

( 5 ) Lin He, Doctor's d i s s e r t a t i o n , Shanghai I n s t i t u t e of Technical P h y s i c s , Academia S i n i c a . 1985.