Study of Electrical Properties of Microcrystalline Silicon Films Using AC Measurements Ely A. T. Dirani 1,2 , Alexandre M. Nardes 1 , Adnei M. Andrade 1 , Fernando J. Fonseca 1 and Reginaldo Muccillo 3 1 LME, Dept. Eng. de Sistemas Eletrônicos, Escola Politécnica da USP, São Paulo,SP, BRAZIL 2 Dept. de Engenharia Elétrica – PUC, São Paulo, SP, BRAZIL. 3 CMDMC, CCTM, IPEN, São Paulo, SP, BRAZIL ABSTRACT Hydrogenated amorphous (a-Si:H) and microcrystalline (μc-Si:H) silicon films are indispensable materials for large area electronic devices like solar cells, image sensors and thin film transistors (TFTs). The interest of the μc-Si:H films arise from the fact that they combine the high optical absorption of a-Si:H and the electrical transport properties close to those of crystalline silicon. In this work we show the correlation between substrate deposition temperature, crystallinity and electrical properties of a-Si:H and μc-Si:H films. The films were prepared by a conventional PECVD (13.56 MHz) RF system from PH 3 /SiH 4 /H 2 gas mixtures in the temperature range of 100 to 250 o C. While phosphorus doped (n) a-Si:H are deposited yielding conductivity values no better than 10 -2 S/cm, (n) μc-Si:H layers deposited at substrate temperature of 250 o C show conductivity values higher than 10 1 S/cm, crystalline fraction up to 80% and Hall mobility of about 0.9 cm 2 . V -1 .s -1 . It was observed that a change in the dark conductivity behavior occurs around 140 o C, with a large increase in the conductivity values. A corresponding increase is not seen in the average grain size and in the crystalline volume fraction, which shows an almost linear increase with the deposition temperature. This stronger influence of the temperature in the electrical characteristics of the μc-Si:H films may be related to the phosphorus activation, which occurs in higher degree at higher deposition temperatures. The correlation among Raman spectroscopy, Hall effect and AC conductivity measurements (frequency range 6 Hz to 13 MHz) shows that the crystalline phase dominates the electrical transport mechanism in μc-Si:H films. Preliminary results of AC measurements indicate that the electrical resistivity of each phase of this material can be determined. 1. INTRODUCTION It has been reported [1-3] that a-Si:H and μc-Si:H films have been deposited at temperatures well below the conventional CVD temperature processes. In order to maintain the properties of certain substrates, Plasma Enhanced Chemical Vapor Deposition process can be tailored. In most cases the existing processes make use of high temperature that may damage polymeric substrates. To develop a low temperature process it is necessary to understand the role played by the deposition temperature in the growth mechanism. This commences with the nucleation of “islands” of deposited material followed by the columnar growth and coalescence, which makes the film more compact and continuous [1,2]. This can be observed by the behavior of the deposition rate that, at first, diminishes with the deposition time until it reaches a saturation value [2-4]. The substrate deposition temperature role in the coalescence process is the energy supply for the neutral molecular fractions or the still ionized radicals adhered to the substrate. Increased mobility permits rearrangements into more stable configurations of the material structure. In cases where the deposition rate is sufficiently low, as is the case in microcrystalline film Mat. Res. Soc. Symp. Proc. Vol. 664 © 2001 Materials Research Society A23.5.1