Subharmonic and chaotic response of periodically driven extrinsic Ge photoconductors

The nonlinear response of cooled extrinsic Ge photoconductors to periodic excitation is experimentally studied. Measured phase portraits, Poincaré sections, and power spectra show subharmonic behavior characteristic of driven nonlinear oscillators including a period-doubling cascade to chaotic oscillation which produces excess broad-band noise with observed noise temperatures as high as ∼${10}^9$ K. The experimental results are in qualitative agreement with numerical simulations of a simple rate-equation model of extrinsic photoconductors.