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273

DISLOCATION DEFECT STATES IN DEFORMED SILICON

J. R. PATEL AND L. C. KIMERLING Bell Laboratories, Murray Hill, N. J. 07974, USA

ABSTRACT Transient junction capacitance measurements on deformed silicon reveal a variety of states after deformation. Upon annealing or following more homogeneous deformation the defect spectrum shows a single broad feature. A state at E(0.38) has been tentatively assigned to defect sites along the dislocation. A broad band of states at H(0.35) is postulated to represent states due to the reconstructed dislocation core.

INTRODUCTION Since the very early work on the electrical behavior of dislocations in semiconductors [1,2,3], there has been a continuous effort to understand their detailed electrical characteristics. Perhaps the most sustained effort in this field has been the work of Haasen, Schr6ter, Labusch and co-workers [4,51 who have shown that dislocations in deformed p type silicon introduce a band of levels at Ev + 0.34 eV for 60' dislocations. Grazhulis et al [61 investigating both n and p type silicon find a band of levels at Ev + 0.42eV and Ec - 0.67eV after deformation. In this paper we consider direct measurements of dislocation levels in deformed silicon using transient junction capacitance measurements performed by Kimerling and Patel [9,10]. EXPERIMENTAL Details of the experiments have been given in [9,10]. Two types of floating zone crystals were used: (a) dislocation-free crystals both n and p type and high and low resistivity (b) crystals containing 105/cm of dislocations. Samples were deformed either in bending or compression in the range 650' - 750'C. Specimens for the capacitance measurements were cut parallel to the primary slip plane and polished and cleaned prior to evaporating a Schottky barrier at room temperature: Au-Pd for n type material and Ti for p type silicon. The principles of the transient junction capacitance technique have been reviewed by Miller et al [11]. In what follows the activation energies to the relevant band edges are denoted as E() for the conduction band and Ho for the valence band. RESULTS The defect state spectrum of n type silicon is shown in Fig. 1. A large number of defect states which act as majority carrier traps are revealed. The complex spectra suggest that a variety of defect states besides dislocations are generated by plastic deformation. In particular a dominant state E(.63) to E(.68), depending on the doping concentration, is always found after inhomogeneous deformation in both n and p type silicon.

274

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100

150

200 250 TEMPERATURE (*K)

Fig. 1. Defect state spectrum of low resistivity n-type silicon.

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Fig. 2. Defect state concentration as a function of local dislocation density under Schottky barrier.

Following an anneal of 1 hr. at 900°C the complex defect spectrum Fig. I simplifies and we observe only one broad pe