A novel III-V CCD structure with intersubband detection for infrared sensing

Date of Completion

January 2000


Engineering, Electronics and Electrical




A new structure to utilize intersubband absorption based on GaAs Inversion Channel technology is proposed. A GaAs CCD structure enables a two dimensional infrared imager. The existing QWIP technology utilizes a series of about 40 quantum wells with the dark current determined by thermionic current over the quantum well barrier. The proposed new structure has one or two quantum wells with dark current limited by the recombination current in the AlGaAs barrier layers. A grating structure as an illumination coupler may be incorporated into the device fabrication sequence to enable the detection of normally incident light. It has been shown that the coupling efficiency maximum occurred when it satisfied the second order Bragg diffraction condition i.e., the pitch size of the grating is half the wavelength. This would allow the normal radiation to be diffracted into the lateral guided waves. A resonant cavity structure is also employed to enhance the absorption to compensate for the reduced number of quantum wells in the new structure. The corresponding reflective spectrum as a function of device thickness was simulated using the TMM Method. In addition, an intersubband absorption model was developed using effective mass, non-parabolicity effects and the redistribution of the density of states in a high field to accurately explain the peak positions of responsivity as a function of temperature in previously published data. To optimize the ICT-QWIP, a model based upon Poisson's equation, which utilized established electron and hole current flow relations, was developed for electrically and optically biased situations. The quantum well's vacancy as a measure of infrared signal level was found to be approximately proportional to the incident optical flux. The solutions in steady state were then used as the boundary values to study the time dependent situations. The on/off time responses of the detectors were explained by the electron dynamics between the charge sheet and quantum wells. Finally, the device fabrication and preliminary testing results are presented. ^