An infrared photodetector is formed of a heavily doped p-type Ge.sub.x Si.sub.1-x /Si superlattice in which x is pre-established during manufacture in the range 0 to 100 percent. A custom tailored photodetector that can differentiate among close wavelengths in the range of 2.7 to 50 microns is fabricated by appropriate selection of the alloy constituency value, x, to establish a specific wavelength at which photodetection cut-off will occur.
A valence band quantum-well structure with a modulation doping for an optical-component implemented in Si technology. With this component, a high quantum efficiency and detection efficiency are accomplished. By way of spatial separation of the doped zone from the almost undoped SiGe quantum well, the Coulomb scattering and the recombination probability of the charge carriers drifting in the externally applied electrical field is greatly reduced at the doping material cores.
A light responsive semiconductor device includes a p-i-n structure incorporating a multiple quantum well structure buried within the intrinsic layer and an external resistance and voltage source serially connected across the device for adjusting a critical wavelength at which the light absorption characteristic of the device dramatically changes. By properly choosing the resistance and/or voltage, the photocurrent changes discontinuously at the critical wavelength and the photocurrent exhibits a hysteresis characteristic. A light responsive structure may include individual, serially aligned p-i-n devices or an integrated, unitary semiconductor body inculding a plurality of p-i-n devices.
An intersub-valence band quantum well detector (52), comprising alternating quantum wells (30') and barriers (32'), provided with differential strain permits obtaining hole mean free paths similar to the electron. Consequently, the gain and responsivity should dramatically increase. In addition, the absorption coefficient should increase, while the noise current should decrease; thus, the quantum efficiency and the detectivity (D*) should increase, compared to a detector without the added differential strain.
A method of selective light detection uses an optical multi-stable device selectively exhibiting a variety of optical multi-stable characteristics for incident light wavelengths or intensities. The device includes an optically serial connection of two optical bistable elements. Each of the optical bistable elements includes a photodiode having a light absorbing layer including a quantum well structure. The photodiodes are reverse biased by respective voltage sources through respective series resistors so that an optical bistable characteristic for incident light wavelength or intensity is achieved for each photodiode. The characteristic of the second photodiode includes four stable photocurrents at respective wavelengths.
