IEEE PHOTONICS TECHNOLOGY LETTERS, VOL. 15, NO. 11, NOVEMBER 2003 1531 Development of a Large High-Performance 2-D Array of GaAs–AlGaAs Multiple Quantum-Well Modulators Uriel Arad, Eddie Redmard, Moshe Shamay, Arkadi Averboukh, Shimon Levit, and Uzi Efron, Member, IEEE Abstract—We present the development of an ultrafast two-di- mensional (288 132 elements) reflection modulator array based on GaAs–AlGaAs multiple quantum-wells embedded in asymmetric Fabry–Pérot structure. The array has low operation voltage ( 4 V), low insertion loss, and high contrast ratio at 846 nm. This array was hybridized to 0.25 um complementary metal–oxide–semiconductor driver providing 256 gray levels resolution at frame rate of 50 kHz (driver limited). Major progress in reducing the severe nonuniformity problem of the cavity resonance wavelength in such devices to less than 3.4 nm variation across a 4-in wafer was achieved. Index Terms—Arrays, excitons, Fabry–Pérot resonators, optical correlators, quantum-confined Stark effect, quantum wells, spatial light modulators, ultrahigh-frequency modulation. I. INTRODUCTION M ULTIPLE quantum-well (MQW) modulator is based on excitonic quantum-confined Stark effect, in which the light absorption depends on applied electric field [1]. In order to control the light absorption, the active quantum wells are placed in the intrinsic layer of a p-i-n diode. MQW modula- tors can be used both as intensity or phase modulators. They are very fast optical devices operating at tens of gigahertz [2] with possible large numbers of modulation levels. For appropriate wavelengths, MQW modulators can be based on the well-devel- oped GaAs–AlGaAs technology. The most common design [3] is to embed the MQW structure into an asymmetric Fabry–Pérot optical cavity, creating an asymmetric Fabry–Pérot modulator (ASFPM). This allows us to obtain very high contrast ratios (CRs) for relatively low voltage swings. The impressive speed of MQW modulators makes them suitable for many optical ap- plications such as optical processors, free-space optical commu- nications [4], optical correlators [5], [6], laser beam control [6], and high density and high capacity data storage [6], high band- width input–output onto a complementary metal–oxide–semi- conductor (CMOS) chip [7]. In this work, we present the devel- opment of an ultrafast, large (288 132 pixels) reflection MQW ASFPM array operating at low voltage ( 4 V), low insertion loss, high CR, and 256 gray-level resolution. Our arrays were Manuscript received February 10, 2003; revised July 2, 2003. U. Arad, E. Redmard, M. Shamay, and A. Averboukh are with Lenslet, Herzelia Pituach 46733, Israel (e-mail: uriel@lenslet.com; www.lenslet.com). S. Levit is with the Department of Condensed Matter, Weizmann Institute of Science, Rehovot 76100, Israel. U. Efron is with the Department of Electro-Optics, Ben Gurion University, Beer Sheva 84105, Israel. Digital Object Identifier 10.1109/LPT.2003.818663 hybridized to a 0.25- m CMOS Si drivers which allow working at up to 50-kHz frame rates for 256 voltage-level resolution. We have achieved major progress in reducing the severe nonunifor- mity growth problem, which normally impedes the development of large MQW ASFPMs arrays. Taking advantage of the modern epitaxial growth technique, we have eliminated the need for the growth of additional layers or additional processes steps as will be described below. Our development followed three phases: 1) ASFPM single-pixel development; 2) modulator matrix development and its hybridization to 0.25- m CMOS Si driver; 3) improvement of the growth uniformity. Below, we briefly review the growth structure, the processing of the optical device, and present the device performance. II. RESULTS The single-pixel design was optimized by an iterative process of growth, measurements, and model simulations. The simulations combined optical, electrical, and electronic aspects. Our final structure was grown in a Varian GEN II single-wafer molecular beam epitaxy (MBE) machine on a semiinsulating 3-in GaAs substrate. The substrate was rotated during the growth in order to improve the spatial uniformity of the layers. The top and bottom mirrors of the ASFPM were composed of quarter-wave reflector stacks of, respectively, two p-type and 25.5 n-type periods of alternating 622.4 of Al Ga As and 706 of AlAs layers. At the wavelength of 847 nm, the bottom mirror had a calculated reflectance of about 99.8% and the top mirror had a calculated reflectance of 50.3%. The intrinsic MQW active region consisted of 26 periods of GaAs–Al Ga As layers. It was embedded in a 4- -long conductive optical cavity of Al Ga As. After the growth, we measured the zero bias reflectivity spectra at several locations, with 1.5-mm steps across the wafer diameter. The measured values of (Fabry–Pérot resonance wavelength) varied from 847 nm at the center of the wafer to 839.5 nm at the edge. The values of (the zero bias heavy hole exciton central wavelength) varied from 835.5 to 834.5 nm. According to our theoretical simulations, the 7.5-nm variation in the indicated a thickness growth nonuniformity of about 1.5%. This estimate was consistent with X-ray measurements of the wafer. We fabricated mm size single pixels, from the central region of the wafer, using four processing steps: p-Ohmic contact, wet pixel etch, n-Ohmic contact, and passivation layer. The completed device exhibited good 1041-1135/03$17.00 © 2003 IEEE