The resolution of distributed photorefractive multiple quantum well devices

Abstract

Photorefractive multiple quantum well ͑PRMQW͒ devices can achieve simultaneously higher resolution and greater sensitivity by distributing several highly trapping low temperature growth ͑LTG͒ layers at different depths in their intrinsic region. This article extends a previously derived analytical model of PRMQW devices to distributed photorefractive devices ͑DPDs͒ that consist of a cascade of smaller MQW regions sandwiched between LTG layers. This enables an understanding of how multiple trapping layers affect the resolution and sensitivity in these DPDs. In addition to an improvement in resolution, the model predicts an enhancement in diffraction efficiency at small grating spacings as the number of subdevices increases for a fixed total DPD length. This result is of significance in designing compact image processing systems that can operate at small grating periods but still be able to achieve a large signal-to-noise ratio for image processing and sensing applications.

Variation of the Thickness and Number of Wells in the CdS/HgS/CdS Quantum Dot Quantum Well System

“…[1][2][3][4][5][6][7] Multiplelayered quantum wells are meanwhile used to build solid-state optoelectronic devices. [8][9][10] The first chemically prepared quantum well system was synthesized in the CdS quantum dot. 1,2 Since its preparation, this quantum dot quantum well (QDQW) system has attracted much attention, both experimentally [11][12][13][14][15][16] and theoretically.…”

“…In recent years, an increasing interest in semiconductor quantum well structures has led to the formation of physically and chemically prepared quantum well systems. − Multiple-layered quantum wells are meanwhile used to build solid-state optoelectronic devices. − The first chemically prepared quantum well system was synthesized in the CdS quantum dot. , Since its preparation, this quantum dot quantum well (QDQW) system has attracted much attention, both experimentally − and theoretically. − …”

Optimizing the design of photorefractive MQW devices

“…We have derived a general expression for the diffraction efficiency as a function of grating spacing for an arbitrary distributed photorefractive device [2]. The equations simplify and can be used for understanding trends when we consider N identical MQW regions of thickness d separated by N-1 internal LTG cladding layers, each of thickness L (and outer cladding layers of thickness U2).…”

“…The MQW regions may be either trapping or intrinsic, with the latter showing improved sensitivity but poorer device resolution. This talk will present a unified way of looking at these different approaches, based on an analytic model that we have developed for device resolution [1,2]. Improved resolution at small grating spacings has been achieved by dividing a single photorefractive device (SPD) into a number of sub-devices, a geometry called the distributed photorefractive device (DPD) [3].…”