Analysis of electron spreadinge effects in pixelless quantum well imaging devices

Abstract

The conversion of infrared images in multiple quantum well infrared photodetector QWIP structure into nonuniform distribution of the current driving a light emitting diode LED is considered using an analytical model The developed model of pixelless QWIP LED imagers takes into account transport processes determining the device op eration The contrast transfer characteristic is derived as a function of the number of quantum wells and the electron capture parameter It is shown that the quality of the up converted images is improved with increasing number of quantum wells The pixel less imaging devices under consideration can e ectively convert long wavelength infrared images into short wavelength infrared or visible images Introduction Integrated quantum well infrared photodetectors QWIPs and light emitting diodes LEDs which convert long wavelength infrared radiation into short wavelength infrared or visible ra diation open up new prospects for infrared imaging devices Recently the concept of pixelless QWIP LED imagers has been proposed A schematic view of the imaging device structure and its band diagram are depicted in Fig This paper deals with a theoretical analysis of the electron e ects in such pixelless imaging devices limiting their image transfor mation performance The following two e ects limit the QWIP LED imager performance laterally uniform injection from the emitter caused by the electron photoexcitation nonuni form in general case from the QWs by means of the redistribution of the potential of di erent QWs and the electron di usion in lateral direction It is shown below that these e ects become insigni cant if the number of the QWs is large enough so that the photoelectric gain is not large and the injected electrons do not reach the LED and the e ective length of lateral di usion in the QWIP and LED parts does not exceed the incident radiation wavelength Spatially nonuniform distributions of the electrons excited from the QWs and nonuniform distributions of the output current density which reproduces the incident image are calculated using the developed analytical model This model accounts for electron injection through the emitter tunneling barrier photoexcitation of the electrons from and their capture in the QWs electron drift and di usion above the inter QW barriers both perpendicular to the QW planes and along of the latters and lateral bipolar di usion in the LED active region