Contactless Deep Level Transient Spectroscopy Using Microwave Reflection
- PDF / 325,137 Bytes
- 6 Pages / 420.48 x 639 pts Page_size
- 31 Downloads / 267 Views
CONTACTLESS DEEP LEVEL TRANSIENT SPECTROSCOPY USING MICROWAVE REFLECTION M. S. WANG* AND J. M. BORREGO** *Hittite Microwave Corporation, Woburn, MA 01801 **Electrical, Computer, and Systems Engineering Rensselaer Polytechnic Institute, Troy, NY 12180
Department,
ABSTRACT Contactless deep level transient spectroscopy using microwave reflection at 35 GHz is presented and it is proved to be a powerful technique for characterizing trapping levels in semiconductors without the necessity of special sample preparation. The technique consists of measuring the transient decay in photoconductivity after a monochromatic light pulse has been applied to the semiconductor. The photoconductivity after the light pulse is caused by emission of carriers from trapping levels filled during the light pulse and by scanning the sample temperature it is possible to determine their activation energy. On Si-implanted layers on LEC grown SI-GaAs substrate we have detected three trapping levels, located at 0.15, 0.18 and 0.27 eV below the conduction band, by using a 1060 nm YAG laser, and one level, 0.13 eV below the conduction band, by using a 633 nm HeNe laser. The technique has been applied to LEC SI-GaAs and no trapping levels have been observed above the EL2 level. INTRODUCTION Characterization of deep levels in semiconductor materials is essential in the semiconductor industrial and research environments. The conventional characterization method, called deep level transient spectroscopy (DLTS), was first instroduced by Lang in 1974 [1] . This technique consists of probing the capacitance transient after an injection of carriers into the depletion layer formed by a p-n junction or a metalsemiconductor barrier. In order for measuring the deep levels in semi-insulating materials, where the measurement of the junction capacitance becomes difficult, optical transient current spectroscopy (OTCS) and photoinduced transient spectroscopy (PITS) were introduced in the late 70's [2,3,4]. Both OTCS and PITS utilize a monochromatic pulsed light to induce excess carriers in semi-insulating bulk materials and then observe photocurrent transients after the light pulse. Although the above methods have been widely used in the university and industry laboratories, it is desirable to have a contactless characterization method because the preparation of metallic contacts can be eliminated and the same wafer can be used for fabrication after characterization. In this paper we will demonstrate a contactless technique which uses microwaves and monochromatic light to characterize deep levels in doped as well as semi-insulating semiconductors. MICROWAVE REFLECTION SETUP The schematic diagram of our measuremnt setup is shown in Figure 1 which is a modification of the microwave setup that we Mat. Res. Soc. Symp. Proc. Vol. 209. 01991 Materials Research Society
524
ATTENMATOR
Fig.l.
Schematic diagram of the photoinduced reflection DLTS measurement setup.
microwave
have been using for characterizing semiconductors [5,6]. The microwave probing beam is genera
Data Loading...
