Raytheon Company

James A Finch

Kenneth Kosai

Scott M Taylor

Stephen H Black

Roger William Graham

Richard H Wyles

Jerry A Wilson

A photodetector () includes a substrate () having a surface; a first layer () of semiconductor material that is disposed above the surface, the first layer containing a first dopant at a first concentration for having a first type of electrical conductivity; and a second layer () of semiconductor material overlying the first layer. The second layer contains a second dopant at a second concentration for having a second type of electrical conductivity and forms a first p-n junction () with the first layer. The second layer is compositionally graded through at least a portion of a thickness thereof from wider bandgap semiconductor material to narrower bandgap in a direction away from the p-n junction. The compositional grading can be done in a substantially linear fashion, or in a substantially non-linear fashion, e.g., in a stepped manner. Preferably the first dopant concentration is at least an order of magnitude greater than the second concentration, and more preferably is at least two orders of magnitude greater. When the first p-n junction is reverse biased, a depletion region () exists substantially only within the second layer, and varying the magnitude of the reverse bias shifts the wavelength at which a maximum spectral sensitivity or responsiveness is obtained. At least one electrical contact is provided for coupling the second layer to a source () of variable bias voltage for reverse biasing the p-n junction. As the magnitude of the bias voltage is changed a wavelength of electromagnetic radiation to which the photodetector is responsive is thus changed. An alternating current signal can be superimposed on the reverse DC bias voltage and a synchronous detection technique used to detect photons corresponding to a certain bandgap energy.

Photodiode having voltage tunable spectral response

A unit cell () of a readout integrated circuit is constructed and operated so as to temporally align an image obtained in a first spectral band with a an image obtained in a second spectral band. A method operates, during a frame period, to sub-frame average a first signal detected in the first spectral band by a multi-spectral detector (), to sub-frame average a first signal detected in the second spectral band by the multi-spectral detector, and to sub-frame average a second signal detected in the first spectral band by the multi-spectral detector. The method then reads out the sub-frame averaged signals for each spectral band. The sub-frame averaged may be read out simultaneously from the unit cell. When sub-frame averaging the first and second signals in the first spectral band the method performs a plurality of consecutive sub-integrations and stores the result of each sub-integration on a first sub-frame averaging capacitance, and when sub-frame averaging the first signal of the second spectral band the method performs a single integration of the second signal, and stores the result of the integration on a second sub-frame averaging capacitance. The first spectral band may correspond to long wavelength infrared radiation (LWIR), and the second spectral band may correspond to medium wavelength infrared radiation (MWIR).

IRFPA ROIC with dual TDM reset integrators and sub-frame averaging functions per unit cell

A photodetector ( ) includes a substrate ( ) having a surface; a first layer ( ) of semiconductor material that is disposed above the surface, the first layer containing a first dopant at a first concentration for having a first type of electrical conductivity; and a second layer ( ) of semiconductor material overlying the first layer. The second layer contains a second dopant at a second concentration for having a second type of electrical conductivity and forms a first p-n junction ( ) with the first layer. The second layer is compositionally graded through at least a portion of a thickness thereof from wider bandgap semiconductor material to narrower bandgap in a direction away from the p-n junction. The compositional grading can be done in a substantially linear fashion, or in a substantially non-linear fashion, e.g., in a stepped manner. Preferably the first dopant concentration is at least an order of magnitude greater than the second concentration, and more preferably is at least two orders of magnitude greater. When the first p-n junction is reverse biased, a depletion region ( ) exists substantially only within the second layer, and varying the magnitude of the reverse bias shifts the wavelength at which a maximum spectral sensitivity or responsiveness is obtained. At least one electrical contact is provided for coupling the second layer to a source ( ) of variable bias voltage for reverse biasing the p-n junction. As the magnitude of the bias voltage is changed a wavelength of electromagnetic radiation to which the photodetector is responsive is thus changed. An alternating current signal can be superimposed on the reverse DC bias voltage and a synchronous detection technique used to detect photons corresponding to a certain bandgap energy.

Growing community of inventors

Santa Barbara, CA, United States of America

James A Finch