AVS 45th International Symposium
    Applied Surface Science Division Monday Sessions
       Session AS-MoM

Paper AS-MoM11
Detection and Passivation of Surface States in InP by Thermally Stimulated Exo-electron Emission Spectroscopy

Monday, November 2, 1998, 11:40 am, Room 307

Session: Materials Analysis (including Small Dimensions and Synchrotron)
Presenter: S.S. Hullavarad, University of Pune, India
Authors: S.S. Hullavarad, University of Pune, India
S.V. Bhoraskar, University of Pune, India
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InP based devices are rapidly becoming dominant in high mobility and optoelectronic device technologies. InP has an electron mobility that is three times that of conventional Si. In principle, devices built with InP should be faster by this factor than the comparable Si devices. However, the surface properties of InP have prevented its use in MIS devices. Devices based on InP suffer from defects that occur in the material which act as charge traps, changing the bias of the device and so impeding its performance. We have attempted to tailor the surface of InP so as to reduce the surface state density by tying up the dangling bonds with proper passivant. The energy distribution and relative densities of such electronically active surface states in InP have been studied using thermally stimulated exo-electron emission spectroscopy (TSEE). This novel and relatively simple technique has high sensitivity for detecting the surface states which is difficult to be assessed by other techniques. Here this technique is successfully used for the first time for detecting the pinned Fermi positions of the Fermi level in n-(100) InP. The TSEE measurements were performed in the high vacuum conditions using channel electron multiplier, in the clean environment. The surface states in InP in the presence of its native oxide were detected when the sample was heated from 175 K to 450 K. TS EE peaks were identified at 207.5 K and 350 K. The energies of these defects were calculated to be 0.43 eV and 0.74 eV respectively. The surface state passivation of pinned Fermi level is achieved by ECR coupled thiophene plasma polymerization. The constituents of the polymerized InP surface were identified using energy dispersive X-ray analysis (EDXAS). Microwave assisted electron cyclotron resonance (ECR) plasma was used to deposit thin films of passivating overlayers. Polythiophene (CH3CH2S) was deposited by injecting the monomer thiophene into the reaction chamber preevacuated to a base pressure of ~ 10-5 Torr. The TSEE spectrum recorded after the deposition of polymer differed from the one which was recorded earlier. The peak in the TSEE appearing at 207.5 K has disappearede. The very fact that this corresponded to the pinned Fermi level in InP show s that the plasma polymer has been effective in chemically passivating the surface.