Winston K. Chan

High‐frequency amplification and generation in charge injection devices

Room‐temperature high‐frequency measurements on a three‐terminal amplifying device based on real‐space hot‐electron transfer between two conducting layers separated by a potential barrier have been performed. The devices grown by organometallic chemical vapor deposition utilize a novel undoped GaAs/AlGaAs heterostructure which, through its dramatically reduced parasitic leakage compared to previous structures, permits, for the first time, operation as a charge injection transistor. The charge injection transistor exhibits true three‐terminal amplification due to real‐space hot‐electron transfer controlled by electron temperature in a high mobility channel. The device demonstrates power and current gains with cut‐off frequencies of 9.8 and 29 GHz, respectively, with maximum current gain of 39 dB. In the negative resistance transistor mode, the same device was found capable of microwave generation up to 7.7 GHz. The frequency response of our device is shown to be limited by RC in the output circuit and meth...

Optically controlled surface emitting lasers

Summary form only give. SELs (surface emitting lasers) whose output power can be modulated by an external light source are reported. The vertically integrated device used is a heterojunction phototransistor (HPT) in series with a SEL so that the amplified photocurrent of the HPT drives the SEL. It is critical that this current exceed the threshold current of the laser with reasonable incident power. Both a linear mode of operation and a bistable mode are found at different voltage ranges. Even though the device has not yet been optimized, an overall optical power gain is observed.<<ETX>>

Junction field‐effect transistor single quantum well optical waveguide modulator employing the two‐dimensional Moss–Burstein effect

A modulation‐doped junction field‐effect transistor incorporating an optical waveguide under the gate modulates light by the carrier band‐filling effect (two‐dimensional Moss–Burstein effect) in a single quantum well, achieving a 5:1 extinction ratio in a 250‐μm‐long waveguide for 4 V reverse gate‐source bias Vgs swing and 0 V drain‐source bias Vds. Similar performance is obtained over a 16 nm spectral range. A novel band‐edge transparency effect is observed for Vds>0 allowing an extinction ratio of 10:1, corresponding to a change in absorption of 92 cm−1 to be obtained through band‐gap dilation by hot electrons at biases of Vds =8 V. Below‐band‐gap refractive index modulation of 1.6×10−3 is obtained for a Vgs swing of 2.4 V. The novel junction field‐effect transistor optical modulator also functions as a photovoltaic or photoconductive optical detector, a transistor, and a light‐emitting diode.

Phase-shifted quarter micron holographic gratings by selective image reversal of photoresist

Nouvelle technique utilisant un photoresist conventionnel et la lithographie optique pour lobtention dun reseau holographique. Application a la fabrication de lasers a reaction repartie

Nonlinear transport phenomena in a triangular quantum well

We have measured transport properties in an AlGaAs/AlxGa1−xAs, triangular quantum well whose energy spectrum has been varied by means of gate bias. We have observed several nonlinear effects in the lateral conductance arising at positive gate voltages as the increasing Fermi level is moved toward the lowering energy positions of the excited subbands in the quantum well. We interpret our results in terms of electron population of the excited subbands in which electrons possess low mobility. Finally, we find new features at high lateral voltages which are considered to be an evidence of previous predicted electrophonon resonance.

Electronically and optically controllable vertical-cavity surface-emitting laser arrays for optical interconnect and signal processing applications (Invited Paper)

Recent progress on vertical cavity surface emitting lasers has spurred interest in them for a wide variety of applications. In this paper, we describe several schemes for achieving the addressing and control of vertical cavity laser arrays required for all applications. Vertical cavity surface emitting laser array design, fabrication, performance and uniformity are discussed. In addition, we report on the first integration of these devices with Si CMOS circuitry. Experimental measurements of perfonnance up to 622 Mbit/s of vertical cavity laser/Si driver circuits are presented. INTRODUCTION Vertical cavity surface emitting (VCSE) lasers have been the subject of substantial interest recently because of their potential for a variety of optical signal processing and optical interconnect applications. In contrast to edge emitting devices, large numbers of VCSE lasers are easily integrated. Devices can be characterized at the wafer level, and processed to form one or two dimensional arrays of arbitrary size and spacing. Recently, both ion beam etching and ion bombardment processing techniques have been used on totally MBE-grown VCSE laser wafers to produce devices with —ma threshold currents, <5V threshold voltages and high differential effiO-8194-0713-5/92/

Microlaser-based compact optical neuro-processors (Invited Paper)

4.OO SPIE Vol. 1582 Integrated Optoelectronics for Communication and Processing (1991) / 83 ciencies[1-4]. There are many issues associated with the potential use of these devices in vanous applications including: implementing control of each laser in an array, uniformity of device characteristics in an array, power dissipation issues, compatibility with electronic interfaces in subsystems and choice of the interconnect medium itself. ELECTRONICALLY ADDRESSED VCSE LASER ARRAYS In this paper we will discuss implementing onand off-chip control of the laser array. The vertical cavity laser structure we use consists of two semiconductor quarter-wavelength stacks which form the n and p-side mirrors sandwiching an InGaAs triple quantum well active region. At the simplest level, electronic control of a VCSE laser array can be achieved through either an independent or matrix-addressing scheme[5,6]. The appropriate addressing depends on a set of application-determined requirements, such as the number, density and geometry of lasers required. Independently addressable arrays up to 16x16 have been fabricated with high yield and excellent uniformity. Figure 1(top) shows the distribution of threshold currents over 8x8 arrays on two different wafers. Figure 1(bottom) shows a typical I-V characteristic, and the distribution of voltages at threshold. Typical outputs for our lasers range up to -2 milliwatts under cw operation at room temperature, limited by device heating. At the drive currents(< 20 ma) needed to achieve these output powers, the operating voltages are <5V. This is important for interfacing to electronic subsystems which will utilized such arrays. Matrix, or row-column addressing offers the advantage of reducing the number of bond pads needed for an NxM array from (NM) to (N+M), and offers potential for achieving very high densities of devices. Figure 2 shows a photo of a top view of a 32x32 matrix-addressed VCSE laser array. The lasers are separated by 100 microns, making the total chip area for the 1024 laser array 3.5x3.5 mm. Recently, we have been able to achieve 99% yields in a matrix-addressed array, and have demonstrated rastering of the device at speeds up to 10 MHz[7]. 84 / SPIE Vol. 1582 Integrated Optoelectronics for Communication and Processing (1991) OFFICALLY CONTROLLABLE VCSE LASER We have also designed and fabricated an optically controilable VCSE laser[8]. Although in the near term, the most likely interconnect scenario will utilize electronically-addressable devices, optically addressed laser arrays may also ultimately be useful, for example, as a repeater element, or in image-based optical signal processing systems. Our optically controllable device, shown schematically in Fig 3, is a vertically integrated VCSE laser-heterojunction phototransistor. It is a two terminal device with co-directional light input and output, is triggerable by a wide range of wavelengths, has an experimentally measured large signal external optical gain of 5, and <100 na dark current. We have demonstrated AND gate operation using this device by adjusting the intensities of two incident beams so that it takes both to trigger the device into the ON state. This monolithically integrated device can also function as a latch[8]. Because it is optically addressed, very large, dense arrays of such devices should be achievable. HYBRID INTEGRATION OF VCSE LASERS WITH SI CMOS A strong requirement for many applications is compatibility with prevalent electronic circuit technologies. As a first step towards integration with Si, 8 Si CMOS drivers and an array of VCSE lasers have been mounted in a hybrid package[9]. The driver design for an array of lasers must be as economical as possible in terms of wafer real estate and power dissipation. For example, the uniformity of threshold current across our laser array was excellent, allowing a common prebias for all 8 lasers. The hybrid delivered 622 Mbit/s operation of the VCSE laser/CMOS driver combination at a bit error rate <10 . Figure 4 shows pseudo random bit pattern-generated output and eye diagrams at both 300 Mbit/sec(top) and 622 Mb /s(bottom.) In order to reduce the parasitics associated with wire bonding, and to make the opticalelectronic interface as simple as possible, we have investigated the use of solder bump-bonding for mounting VCSE laser arrays on arbitrary substrates. To date we have successfully flip-chip bonded a 2x8 laser array to a high speed mount, demonstrating 5 Gbit./s operation for each of SPIE Vol. 1582 Integrated Optoelectronics for Communication and Processing (1991) / 85

Langmuir-Blodgett Deposited Gates For InP-InGaAs Field Effect Transistors

This paper reviews the recent progress in the development of holographic neural networks using surface-emitting laser diode arrays (SELDAs). Since the previous work on ultrafast holographic memory readout system and a robust incoherent correlator, progress has been made in several areas: the use of an array of monolithic `neurons to reconstruct holographic memories; two-dimensional (2-D) wavelength-division multiplexing (WDM) for image transmission through a single-mode fiber; and finally, an associative memory using time- division multiplexing (TDM). Experimental demonstrations on these are presented.

Phase-shifted gratings by selective image reversal of photoresist

We report on the novel application of Langmuir-Blodgett film deposition of cadmium di-stearate to form a high barrier height Schottky barrier on n-In0.53Ga0.47As. The method is simple and can be applied to integrated optoelectronics where conflicting device requirements impose astringent constraints on the material and processing technology. Using this technique to form the gate electrode, we fabricated a 1μm gate length inverted InP-InGaAs modulation doped field effect transistor (MODFET) with an extrinsic transconductance of 170 mS/mm and a current gain cut-off frequency fT of 19 GHz.