Appl. Phys. A55, 378-386 (1992) Applied .o,,.. Physics A "" Surfaces © Springer-Verlag 1992 Microwave Detected Transient Photoconductivity Measurements During Plasma Deposition of Intrinsic Hydrogenated Amorphous Silicon H.C. Neitzert and M. Kunst* Hahn-Meitner Institut, Dept. Solare Energetik, Glienicker Strasse 100, W-1000 Berlin 39, Fed. Rep. Germany (Fax: +49-30/8009-2434) Received 4 November 1991/Accepted 13 May 1992 Abstract. Contactless in-situ measurements of the micro- wave detected transient photoconductivity during growth of intrinsic a-Si:H films by plasma enhanced chemical vapour deposition are presented. It is shown, that these measure- ments can be performed without perturbation of the deposi- tion process.The growth of a-Si:H films at 250 ° C and 120 ° C substrate temperature is studied and the information obtained from these measurements is discussed. In-situ characteriza- tion during growth of a multilayer structure with films de- posited subsequently at 120 ° C, 250°C and again at 120°C is shown. PACS: 73.60.Fw, 72.80.Ng The deposition process of hydrogenated amorphous silicon is controlled by a variety of adjustable process parameters and other more or less unpredictable influences. In-situ determi- nation of the properties of the growing layer seems necessary for a deeper understanding and for control of the deposition process. It turned out to be a difficult task to correlate plasma parameters like electron temperature, electron density, dis- tribution and type of the ionized species directly with the optoelectronic properties of the as-grown a-Si:H layers. In the last years more emphasis is given on the direct charac- terization of the growing layers during the deposition. Ellip- sometry for example has been shown to give more insight into the early stage of a-Si:H deposition by determining the optical constants of the films and correlating them with structural properties [1,2]. Recently, in-situ infrared eUip- sometry [3], and infrared reflection absorption spectroscopy [4] enabled even direct observation of the hydrogen bonding configurations in thin layers during the growth. The application of amorphous silicon in electronic de- vices is still limited by the poor charge carrier transport properties and much effort is made in improving the elec- tronic transport properties of these layers. Therefore, in-situ * To whom all correspondence should be addressed measurements giving information about the electronic struc- ~ture of the material are of particular interest. Kelvin probe measurements are used for determining the surface potential but the plasma process has to be interrupted for these mea- surements [5]. Time-of-flight measurements are so far one of the most important techniques for determining the mobility- lifetime product in amorphous silicon but these measure- ments cannot be performed during deposition. Transient pho- toconductivity measurements have been shown to give simi- lar information about charge carrier kinetics. The microwave detected transient photoconductivity (TRMC) technique [6] as a contactless measurement method has shown its feasi- bility for in-situ application [7]. Here, we will present in-situ TRMC-measurements dur- ing the growth of intrinsic amorphous silicon. 1 Experimental Intrinsic hydrogenated amorphous silicon (a-Si:H) films were deposited in a conventional capacitively coupled glow discharge deposition system on 0.5 mm thick Coming 7059 glass substrates using undiluted silane under the following conditions: A deposition temperature (Tdep) of 250 ° C, a silane flowrate (FsiH4) of 10 sccm, a gas pressure (Pdep) dur- ing deposition of 35 Pa, radio frequency (rf)-power-density of 25 mW/cm 2 and self-biased. During the deposition the change of the microwave re- flection after pulsed laser illumination has been followed, using the setup schematically shown in Fig. 1. The deposi- tion system is made from stainless steel and can be evacu- ated by~a turbomolecular pump down to a pressure of less than 10 -5 Pa before deposition to avoid residual gas con- tamination. The electrodes of the glow discharge system are two stainless steel cylinders of a diameter of 5 cm which are placed at a distance of 2.5 cm. The glass substrate is placed on the grounded electrode, which can be heated, and termi- nates the end of an open waveguide. The temperature of the substrate electrode is measured by a thermocouple close to the surface and the difference between the measured tem-