Increasing the Near Infrared Photodetection Efficiency of Hyperdoped

Date of Award

8-1-2024

Degree Name

Ph.D. in Electro-Optics

Department

Department of Electro-Optics and Photonics

Advisor/Chair

Jay Mathews

Abstract

Hyperdoped Si materials extend Si response range into near infrared by forming intermediate band in Si band gap. Au and Ti as deep levels in Si have potentials to achieve sub bandgap photodetection. To achieve commercialized Au-hyperdoped Si (Si:Au) photodetectors, we enhance its optical absorption by changing the conditions of ion implantation and pulsed laser melting and demonstrated possible routes to form Ohmic contact to Si:Au. In chapter 3, we showed Boron doping benefits contacts to the highly resistive Si:Au materials. Metal Pt and Ni both decrease the contact resistivity compared to Au contact. Ti or Cr, as the interfacial layer, decreases the barrier height between metal and Si:Au. We also demonstrate that CrSi formation temperature is higher than that of dimer substitutional states of Au in Si. The Au hyperdoped Si photodiodes have been demonstrated feasible for infrared photodetection. But the efficiency is low because of the unreasonable structure and fabrication process. In this paper, we optimized the Si:Au photodiodes depletion region to increase sub bandgap efficiency to 4.4×10^(-3) at 1550nm. The cutoff energy of is correspond to the Au acceptor level instead of defects. The origin of the response gain is not clear. Thermal annealing doesn’t improve the efficiency of photodiodes but extended the response cutoff energy to longer wavelengths. The ionization rate of Ti in Si is high enough to compensate the carrier in Si substrate and shows n-type behavior. Ti:The Ohmic contact routes to Si:Ti are reported. Al contact shows relative low contact resistivity (1.2-4.43Ωcm2) and the degenerate contact doping doesn’t help to improve the contact behavior. The surface of Si:Ti has strong fermi pining effects and the surfaces states manipulating is important to decrease the barriers height. Ti hyperdoped Si (Si:Ti) has been demonstrated to have sub bandgap photo response. In chapter 6, we fabricated and characterized the Si:Ti photodiodes and optimized the structure. In room temperature, the 3.5×10-3 EQE has been obtained at telecommunication wavelength 1550nm. And the detectable response extends up to 2250nm. The results show the potential of Si:Ti materials being both Si:Ti photovoltaics and commercialized IR detection. To improve the efficiency of Si:Ti photodetectors, the affection of absorption rate, devices structure and the Si:Ti crystal quality has been discussed. The photo response of Si:Ti photodiodes may come from the defects instead of the substitutional Ti. Photoconductive gain has been demonstrated in the optimized Si:Ti photodiode which benefits the devices efficiency.

Keywords

Electrical Engineering; Materials Science; Optics

Rights Statement

Copyright © 2024, author.

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