Electrical properties of electron- and proton ... - Wiley Online Library

8 downloads 954 Views 155KB Size Report
V.D. Kuznetsov Siberian Physico-Technical Institute,. State University, Tomskl) (a) and A. F. Ioffe Physico-Technical Institute,. Academy of Sciences of the USSR, ...
Short Notes

K191

phys. stat. sol. ( a ) % K191 (1984) Subject classification: 11 and 14.3; 22.2.1;

22.8

V.D. Kuznetsov Siberian Physico-Technical Institute, State University, Tomskl) (a) and A. F. Ioffe Physico-Technical Institute, Academy of Sciences of the USSR, Leningrad21 (b) Electrical Properties of Electron- and Proton-Irradiated GaAs and ZnGeAs2 Solid Solutions BY V.N. BRUDNYI (a), M.A. KRTVOV (a), A.I. FWI'APOV (a), and YU.V. RUD (b) The solid solutions of GaAs and ZnGeAs2 attract attention as new semiconducting compounds for light emitting source fabrication. But up t o now these solutions are obtained a s p-type samples only with high free hole concentration 19 (p l x l 0 ~ m ' ~and ) low resistivity (Q 5 to Qcm) at room temperature (RT). The attemnts t o control the electrical properties of these solutions by chemical doping o r by changing of sample growing conditions were unsuccess-

-

ful. It is assumed that the behaviour of such samples is modified by the grownr

in Jattice defects of non-stoichiometric and disorder origin, such as [GeAs], [GaGd, [Zr+-.d,

vacancies and interstitial atoms.

The present study is undertaken t o investigate the influence of high energy electron- and proton-bombardment induced lattice defects on the electrical properties of GaAs and ZnGeAs2 solid solutions. The virgin polycrystalline samples with (2 GaAs):ZnGeAs2 = 2:l and 4:l compositions are obtained by melting of elements in nearly stoichiometric ratio with subsequent crystallization. The samples with (2 G a b ) : ZnGeAs2 = 1:l composition are produced by hardening at 1100 OC. All investigated samples of sphalerite modification have p-type conductivity and resistivity of about 4 t o 6X10-3 Qcm in the temperature range from 77 t o 300 K. The wafer specimens are polished t o about 100 p m (for 5 MeV proton bombardment) and t o about 500 p m (for 2 MeV electron bombardment) and chemically etched in a HF:HN03 = 1:3 solution during 5 s at RT to remove surface dam-

ages.

Indium contacts (340 OC, 900 s) a r e used for electrical measurements.

1) pl. revolutsii 1, 634050 Tomsk, USSR.

2 ) Politekhnicheskaya 26, 194021 Leningrad, USSR.

K192

physica status solidi (a) 82

Fig. 1. Change of resistivity with 2 MeV electron, (A, A, +), 5 MeV H+ ion (0,. ,V), and 175 keV H+ ion ( ) bombardment in l ( 2 GaAs): ZnGeAs2 &A, V , n), 2(2GaAs):ZnGeks ( + ) , and 4(2GaAs):ZnGeAs2 (0,. ). A , o , V , o , + RT;A, 0 7 7 2 Fig. 2. Temperature variation of resistivity in initial ( A ), 2 MeV electron (A, ), 5 MeV H+ ion ( o ), and 175 keV H+ ion ( x ) irradiated samples of 1 (2GaAs):ZnGeAs2 (A,X ), 2(2GaAs):ZnGeAs2 ( 0 ), and 4(2GaAs):ZnGeAs ( A , o ~ x , o , o , A afterirradiationupto1016,

2-2 1.5xlOl8, a n d 1 0 l 9 c m ,

respectively

The samples were irradiated at RT by H+ ions (175 keV, 5 MeV) up to a cumulative fluence of 1x10' fluence of l x l O 1 '

cm'2 and by electrons (2 MeV) up to a cumulative

cm-2. The effect of electron and proton bombardments on the

resistivity of the investigated samples is shown in Fig. 1. The mean value of resistivity kc

2

Q increases with fluence achieving the values % 10 8 c m at RT and

106 Qcm at 77 K. This is attributed t o free hole'frapping by radiation-in-

duced donor-type defects. These results indicate that G a k s and ZnGeAs2 solid solutions change their electrical properties at electron and proton irradiations in the same way as the earlier investigated binary GaAs /1, 2/ and ternary ZnGeAs2 13, 41 compounds. In Fig. 2 the temperature variations of resistivity for several bombardment steps is shown f o r some samples. In virgin samples impurity conduction is realised in the temperature range from 77 K t o RT. In irradiated samples the temperature dependence of Q near RT can b e expressed by

-9 (T 1

N

exp(E/kT)

Short Notes

K193 Fig. 3. Isochronal (600 s) annealing of resistivity in 1(2 GaAs): ZnGeAs2 ( A ) and 4 (2 G a b ) : ZnGeAs2 ( 0 ) after electron (lo1' cm-2) ( A ) and 5 MeV 17 H+ ion (10 cme2) ( 0 ) irradiation at RT

Here E is the activation energy of this conduction mechanism. The E value increases upon irra-

?i"("LI

-

diation from

0 in virgin samples up t o r4 0.15 eV in heavily irradiated samples. The increase of E W

due t o irradiation is attributed to a shift of the

F e r m i level towards midgap. Post-irradiated isochronal annealings of in 1 (2 GaAs):ZnGeAs2 and 4(2 GaAs): ZnGeAs2 samples are shown in Fig. 3. In electron-irradiated samples the resistivity recovers in three well-defined stages near 150, 200 t o 300, and 400 t o 500 OC. These s t a g e s are well coinciding with annealing stage positions in electron-irradiated GaAs /1/ and ZnGeAsZ /3/ compounds. restored in two In proton-irradiated GaAs and ZnGeAs2 solid solutions, stages at about 200 t o 300 OC and 400 t o 500 OC, and these results are in good accordance with the restoring of electrical properties in proton-irradiated GaAs /2/ and ZnGeAs2 /4/ samples. The annealing experiments indicate that donor-type defects are annealed in the temperature range 20 to 500 OC in electron- and proton-irradiated GaAs and ZnGeAs2 solid solutions. It can b e concluded from the presented results that electron and proton bombardments a r e useful for insulating region fabrication in solid solutions of GaAs 2 and ZnGeAs2. Semi-insulating layers with Q 5 10 Qcm at RT and with 2 1 06 Q c m at 77 K could be produced after high-energy particle bombardment at RT.

/l/V.N.

References BRUDNYI, M.A. KRIVOV, A.I. POTAPOV, and V.I. SHAKHOVTSOV,

Fiz. Tekh. Poluprov. g, 40 (1982). /2/V.N. BRUDNYI, M.A. KRIVOV, and A.I. POTAPOV, Izv. vuzov, Fiz.

3

39 (1982). /3/ V.N. BRUDNYI, M.A. KRIVOV, A.I. POTAPOV, and YU.V. RUD, Izv.

physica status solidi (a) 82 vuzov, Fiz.

2,

121 (1982). /4/V.N. BRUDNYI, A.I. POTAPOV, and YU.V. RUD, phys. stat. sol. (a) 75, K73 (1983). (Received December 5, 1983)