High-resolution spatial light modulators using GaAs/AlGaAs multiple quantum wells

Bowman, S. R.; Rabinovich, W. S.; Kyono, C. S.; Katzer, D. Scott; Ikossi‐Anastasiou, K.

doi:10.1063/1.112160

Cited by 26 publications

(12 citation statements)

References 6 publications

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“…Lateral drift can be overcome by deep-level defects introduced in the MQW region that trap carriers before they move significantly in the lateral direction. To achieve this in GaAs/ AlGaAs devices, Cr doping, 3 proton implantation, 8,9 and low-temperature growth 4,10 ͑LTG͒ have been employed.…”

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confidence: 99%

“…A square voltage of amplitude 20 V was applied across the device at a 50% duty cycle, with a repetition rate that was optimized for maximum peak diffraction efficiency in each device. The diffracted signal from a Stark-geometry device is always transient, 4,8,9,10 since some fraction of the carriers accumulate in the dark regions ͑albeit at a slower rate with respect to the bright regions͒ and the applied field is eventually screened everywhere, washing away the grating. Thus, the peak input diffraction signal was recorded versus the grating period, as shown in Fig.…”

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confidence: 99%

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Photorefractive multiple quantum well devices approaching diffraction-limited resolution

Abeeluck

Garmire

Canoglu

et al. 1999

Applied Physics Letters

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We demonstrate that a resolution approaching their fundamental drift-free diffraction limit can be achieved in photorefractive multiple quantum well (MQW) devices by proper choice of the growth and anneal conditions. Previously reported devices are compared with four MQW samples grown at low temperature and annealed after growth at 620 °C for over 3 h. A simple analytical model with and without lateral drift of photocarriers is used to explain the observed experimental resolutions. The growth temperature and annealing procedure of the low-temperature-grown MQW are shown to significantly influence the device resolution by reducing lateral drift.

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Photorefractive multiple quantum well devices approaching diffraction-limited resolution

Abeeluck

Garmire

Canoglu

et al. 1999

Applied Physics Letters

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“…2 These devices use multiple quantum wells that have been made semi-insulating by ion implantation 2 or chromium doping. 1 An ac electric field is applied perpendicular to the plane of the wells at a rate faster than the dark screening time of the material.…”

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“…To produce the grating interference pattern we used an achromatic grating arrangement. 2 The first order diffraction of one of the pump beams was measured using a silicon pin photodiode.…”

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Intrinsic multiple quantum well spatial light modulators

Rabinovich¹,

Bowman²,

Katzer³

et al. 1995

Applied Physics Letters

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Large improvements are reported in the sensitivity of optically addressed multiple quantum well spatial light modulators. In prior work with these materials the quantum well region has been made semi-insulating. It is shown that this is unnecessary and in fact detrimental to performance. By placing layers containing high trap concentrations at the ends of the structure and leaving the active quantum well layers intrinsic the speed of the device at a given illumination is improved by more than four times, diffraction efficiency is enhanced and spatial resolution is almost the same. © 1995 American Institute of Physics.Recent demonstrations of perpendicular geometry GaAs/ AlGaAs multiple quantum well ͑MQW͒ structures as optically addressed spatial light modulators ͑OASLM͒ have shown that these devices can offer high speed 1 and high resolution. 2 These devices use multiple quantum wells that have been made semi-insulating by ion implantation 2 or chromium doping. 1 An ac electric field is applied perpendicular to the plane of the wells at a rate faster than the dark screening time of the material. The surface of the quantum well is then exposed to a write beam that creates photocarriers which screen the applied field in the illuminated regions. The result is an internal electric field which is modulated in the same pattern as the write beam. The optical properties of the quantum well are then changed through the quantum confined Stark effect, and readout with a beam that is nearly resonant with the heavy hole exciton.All MQW OASLMs to date have had deep traps distributed throughout the MQW region. These ''bulk'' traps have been thought necessary to decrease the dark conductivity of the MQW layers so that screening is largely due to photogenerated, and not background, carriers. In addition, the bulk traps were included to restrict the lateral diffusion of carriers which degrades OASLM resolution. Both these motivations are valid for parallel field geometry MQW OASLMs where photogenerated carriers drift and are trapped within the quantum well layers. 3 This thinking may not, however, apply to the perpendicular geometry for two reasons: First, materials grown by molecular beam epitaxy ͑MBE͒, can have an unintentional doping on the order of 10 14 carriers/cm 3 . This doping concentration is sufficient to screen only about 10% of the high fields applied to these materials in the perpendicular geometry ͑ϳ50 kV/cm͒. Any further screening must be by photocarriers or thermally generated carriers, of which there are few due to the large band gap of GaAs. Thus, background carrier screening may not be a problem in good quality materials.Second, recent work also suggests that bulk traps may not be necessary to maintain OASLM resolution. Theoretical calculations indicate that the screening carriers accumulate in an extremely thin ͑5 nm͒ region at the semiconductorinsulator interface. 4 In addition, experimental measurements of MQW OASLMs indicate that the transit time of the carriers across the quantum well region is ϳ300 ps, 5...

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“…After annealing, excess As atoms group together to form As clusters [5,6). A large amount of research work has been performed on the defects [7][8] in LT grown materials and their effects on 'photorefractive device parameters [9][10][11]. However, it is an open question what dependence the characteristics of LT MQWs materials and features of their photorefractive devices have on the type, density and structure of the defects.…”

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Optimizing features of photorefractive devices by tailoring native defects incorporated in the GaAs/AlGaAs multiple quantum wells

Han¹,

Guo²,

Bao³

et al.

COMMAD 2000 Proceedings. Conference on Optoelectronic and Microelectronic Materials and Devices

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To study the influence of defects on device effect, low temperature (LT) grown GaAs/AIGaAs multiple-Quantum-wells (MQWs) were grown under different As pressure for the use in a stark geometry device. The differences in the samples are their defect density in the MQW region. By comparing optical properties, it was found that the optimum device effect coming from high optical quality obtained from samples grown at a critical condition. The detailed defect characteristics and optical properties of the samples with different excess As have been discussed. A. IntroductionMedium low-temperature (LT) grown GaAs/ AIGaAs MQW structure was the most widely used material for Stark-geometry MQW photorefractive devices [1-4). It is generally believed that excess As is incorporated into the epilayer in the form of As anti site (AsGa), Ga vacancy (V Ga) and As interstitial (Asi) during the low temperature growth. After annealing, excess As atoms group together to form As clusters [5,6). A large amount of research work has been performed on the defects [7][8] in LT grown materials and their effects on 'photorefractive device parameters [9-11]. However, it is an open question what dependence the characteristics of LT MQWs materials and features of their photorefractive devices have on the type, density and structure of the defects. High defect density usually broadens the excitonic spectrum, and as a result of which, the electroabsorption (EA) decreases greatly.Here, in order to obtain sharp excitonic absorption, the relation of optical properties and device features with defects was analyzed. B. ExperimentsThree samples (sample A, B, and C) were grown with the structure reported previously [4] in a V80 MBE system. As pressure of 1.7x 10-7, 2.63x 10-7 and 3.7xlO-7 Torr were used for the multiple quantum wells in sample A, B and C while As pressure 'used for trap-layers was 5.0xlO-7 Torr. After growth, the samples were subjected to 30s rapid thermal annealing (RTA) from 500 to 800°C. The absorption and electroahsorption of devices were measured at 300K [4], and the photoluminescence (PL) from samples were detected at 17K under an excitation optical source of Ar + laser.

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High-resolution spatial light modulators using GaAs/AlGaAs multiple quantum wells

Cited by 26 publications

References 6 publications

Photorefractive multiple quantum well devices approaching diffraction-limited resolution

Photorefractive multiple quantum well devices approaching diffraction-limited resolution

Intrinsic multiple quantum well spatial light modulators

Optimizing features of photorefractive devices by tailoring native defects incorporated in the GaAs/AlGaAs multiple quantum wells

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