Doping - Spike PtSi Schottky Infrared Detectors with Extended Cutoff Wavelengths

1. ABSTRACT. * A technique incorporating a p+ doping spike at the silicide/Si interface to reduce the effective Schottky barrier of the silicide infrared detectors and thus extend the cutoff wavelength has been developed. In contrast to previous approaches which relied on the tunneling effect, this approach utilizes a thinner doping spike (< 2 nm) to take advantages of the strong Schottky image force near the silicide/Si interface and thus avoid the tunneling effect. The critical thickness, i. e., the maximum spike thickness without the tunneling effect has been determined and the extended cutoff wavelengths have been observed for the doping-spike PtSi Schottky infrared detectors. Thermionic-emission-limited and thermally-assisted tunneling dark current characteristics were observed for detectors with spikes thinner and thicker than the critical thickness, respectively. 2. ,. L INTRODUCTION Silicide Schottky infrared (IR) detectors offer promise of a low-cost, rugged, medium wavelength infrared (MWIR) thermal imaging technology with advantages in silicon-based fabrication, producibility, array size, response uniformity, and low I/f noise [1]. State-of-the-art 640 x 480-and 1024 x 1024-element PtSi focal plane arrays, with cutoff wavelengths ranging from 5.1 to 5.9 pm, are used for imaging in the 3-5 pm medium wavelength infrared (MWIR) region[2-5]. The spectral response of the silicide Schottky IR detector follows the modified Fowler equation, given by (hv-YO)2 q=cl hv)=1.24C11 ?@ c (1) where ~ is the quantum efficiency (QE), Cl is the emission coefficient, hv and k are the energy and the wavelength of the incident photon, respectively, Y?. is the optical potential barrier, and ~ is the cutoff wavelength, given by (2) There is a great interest in extending the PtSi cutoff wavelength for long wavelength infrared (LWIR) operation in the 8-14 pm regime and for improved M WIR performance as given by Eq. 1. Previously, we have demonstrated extended PtSi cutoff wavelengths ranging from 5.7 to 22 pm by incorporating a thin (< 1.1 nm) p + doping spike at the PtSi/silicon interface [6,7], As shown in Fig. 1(a), the effective Schottky bai-rier height is determined by the combined effects of the image-force effect and the electric field of the depletion region, This doping-spike technique takes advantages of the strong Schottky image force within-2 nm from the PtSi/Si interface, as shown in Fig. 1 (b). The barrier reduction AY due to the introduction p+ doping spike can be given approximately by I ,. where N and d are the doping concentration and …