Grain Boundary States in Float-Zone-Si-Bicrystals
- PDF / 371,345 Bytes
- 11 Pages / 420.48 x 639 pts Page_size
- 4 Downloads / 196 Views
GRAIN BOUNDARY STATES IN FLOAT-ZONE-SI-BICRYSTALS G. PETERMANN AND P. HAASEN Institut f. Metallphysik, Universitat Gi5ttingen, and SFB 126, Hospitalstr. 3-5, D-3400 G5ttingen, F. R. Germany
ABSTRACT A near E25 grain boundary has been studied electrically in FZ-silicon at various degrees of n-doping. The boundary is electrically active without previous heat treatment. A unique density-of-states can be derived from dc and ac measurements at all dopings and temperatures investigated. The model of the charged g.b. includes potential fluctuations in the g.b. plane. Admittance spectroscopy allows to differentiate between g.b. states and deep centers its the compensating space charge zone.
INTRODUCTION We have for some time studied the electrical properties of various symmetrical bicrystals in n- and p-type germanium and have found [1,2] an extremely simple electronic structure of the (011) rotated grain boundaries (g.b.): While the 09 g.b. is electrically inactive in n- and p-Ge as are the other investigated zilon (113), (z11-3°), (z9-4 0 ) g.b.'s in p-material, these boundaries in n-Ge are described by two acceptor levels ETI 2 =0. 16 and 0.10 eV above the valence band (density of states NT2 =4.5"10l cm- 2 ). The dc (current-voltage characteristics) and ac (HF capacitance) results on Ge agree well with each other below 200K if the theoretical value of the Richardson constant is used while above that temperature they deviate unless an inversion-layer at the g.b. is taken into account. In siliconthe results reported in the literature are much more complex, apparently due to the effects of g.b. contamination as evidenced by the influence of heat treatment, for a review see [3]. Most of the results are on CZ silicon bi- and polycrystals anyhow and their g.b.'s show electrical activity only after a high temperature anneal which is interpreted as an impurity effect due to oxygen [4] or copper [5]. Well defined bicrystals have rarely been investigated neither has the cleaner FZ-silicon [6]. Such a study will be described in the following using dc as well ac measurements (admittance spectroscopy). They are evaluated in one and the Mat. Res. Soc. Symp. Proc. Vol. 106. 4 1988 Materials Research Society
66
same model with a minimum of assumptions, avoiding e.g. an adjustable Richardson-"constant" [7], but including potential fluctuations in the g.b. plane [8,9,10] as well as deep centers in the space charge zone (SCZ) [11].
MATERIALS AND METHODS Two bicrystals of FZ-Si grown in Grenoble under vacuum (FI) and in argon (FII) and supplied by G. Landwehr were investigated. They contained initially ND=9.5x10 12 and 5x101 2 donors/cm3 , respectively. The g.b. is described approximately by a 16.260 rotation around [001] and a (710) plane, which is close to z25 coincidence. Parts of the bicrystal were neutron transmutation-doped to ND=1.4-10 14 /cm3 (F18, F19) and 1.4-10 15 /cm3 (FI1O). After neutron irradiation these specimens were annealed I h at 730 0C under high purity argon. To check the annealing effect itself without irradiat
Data Loading...
