The integration of InGaP LEDs with CMOS on 200 mm silicon wafers

The integration of photonics and electronics on a converged silicon CMOS platform is a long pursuit goal for both academe and industry. We have been developing technologies that can integrate III-V compound semiconductors and CMOS circuits on 200 mm silicon wafers. As an example we present our work on the integration of InGaP light-emitting diodes (LEDs) with CMOS. The InGaP LEDs were epitaxially grown on high-quality GaAs and Ge buffers on 200 mm (100) silicon wafers in a MOCVD reactor. Strain engineering was applied to control the wafer bow that is induced by the mismatch of coefficients of thermal expansion between III-V films and silicon substrate. Wafer bonding was used to transfer the foundry-made silicon CMOS wafers to the InGaP LED wafers. Process trenches were opened on the CMOS layer to expose the underneath III-V device layers for LED processing. We show the issues encountered in the 200 mm processing and the methods we have been developing to overcome the problems

High quality metamorphic graded buffers with lattice-constants intermediate to GaAs an InP for device applications

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 2009.Includes bibliographical references (p. 152-155).We have investigated the use of a continuous, linear grading scheme for compositionally-graded metamorphic InxGal-As buffers on GaAs, which can be used as virtual substrates for optical emitters operating at wavelengths > 1.2 gm. Such virtual substrates will allow access to new materials that can be used for designing optical and electronic devices with superior characteristics and performances compared with conventional devices that are grown lattice-matched on standard substrates such as GaAs and InP. In addition, the principles behind such graded buffers can be used to bridge different lattice-constants, which can be a pathway to future integration of previously distinct classes of devices that have been defined by the lattice-constant on which they were built (e.g. Si-based, GaAs-based, InP-based etc.). Graded buffers with threading dislocation densities (TDD) < 9.5 x 104 cm-2, at a final composition of x = 0.346 were obtained, representing the lowest value ever achieved at or around this composition. Photoluminescence (PL) measurements were carried out on InGaAs quantum wells (QWs) that were re-grown on these buffers, and high luminescence efficiency was observed in the 1.2-1.5 tm wavelength range. Ridge waveguide QW-separate confinement heterostructure lasers and heterojunction bipolar transistors (HBTs) were also grown on the graded buffers to demonstrate their applicability for device applications. Pulsed threshold current densities of 262 Ac2 at room temperature were obtained for 2 mm long strained-InGaAs QW emitting at 1320 nm, with peak output powers up to 40 mW. Preliminary tests on the unoptimized HBTs revealed that they operate with dc current gains of up to 13. A new class of graded buffers using all-binary III-V semiconductors has also been demonstrated. Thin constituent layers of GaAs and InP are combined such that they act in a mechanically-similar fashion as a random alloy.(cont.) We term this combination of many thin layers of constituent materials a Digital Metamorphic Alloy (DMA). The DMAs are used to replace conventional random-alloys in a metamorphic buffer layer. Such a DMA buffer has superior thermal conductivities to, and avoids materials growth-related problems associated with, conventional compositionally-graded random-alloy metamorphic buffers. The method of fabricating DMAs is described. Lattice-constant grading from GaAs to InP has been carried out using both the DMA concept, and a hybrid random-alloy-buffer/DMA approach.by Kenneth Eng Kian Lee.Ph.D

Time- and wavelength-interleaved optical pulse train generation based on dispersion spreading and sectional compression

A method to generate time- and wavelength-interleaved optical pulse trains based on dispersion spreading and sectional compression is proposed and demonstrated. A 4×2  GHz time- and wavelength-interleaved pulse train is generated from an input 2 GHz mode-locked pulse train. The advantages of the proposed scheme are its simplicity and robustness, since no microwave component or multiwavelength laser source is required. In addition, we demonstrate supercontinuum generation of an ultraflat 18 nm bandwidth spectrum with less than 0.5 dB fluctuation over the 3.2 nm central bandwidth.Published versio

The role of AsH[subscript 3] partial pressure on anti-phase boundary in GaAs-on-Ge grown by MOCVD ? Application to a 200mm GaAs virtual substrate

We demonstrate the influence of the arsine partial pressure (p(AsH3)) on the quality of a GaAs layer grown on Ge substrate by metal organic chemical vapor deposition. The GaAs quality improves with p(AsH3) used during the 100 nm thick GaAs buffer layer. By growing a GaAs buffer layer at 630 °C with p(AsH3) of 5 mbar, we obtain a smooth GaAs layer with a root mean square roughness of 4.7 Å. This GaAs layer does not contain anti-phase boundaries. With these optimized growth parameters, we fabricate a virtual GaAs substrate on a 200 mm silicon wafer as a first step towards the integration of III–V devices on silicon.National Research Foundation of Singapor

Frequency-tunable millimeter-wave generation technique based on spectral-filtering of a supercontinuum source

In this paper, we show analytically for the first time that spectral-filtering a supercontinuum source into equally-spaced optical combs with identical comb profile can lead to the generation of frequency-tunable microwave signals. Through simulations, we observe that the frequency of the generated microwave signal can be of any integer multiple of the supercontinuum source's repetition rate which is within the bandwidth of the photodetector used. Using a photodetector with a larger bandwidth enable the generation of millimeter-wave signal

Linearization of an optically sampled analog-to-digital converter

In this paper, we show experimentally for the first time a 2 GSamples/s optically sampled analog-to-digital converter based on dual-output modulation and balanced photodetection scheme. Linearization in the form of arcsine operation is also described to illustrate the considerations of the proposed scheme. Finally, arcsine operation is digitally implemented on the output of the electronic ADC and is shown to enable significant odd-order harmonic suppression at high modulation depths approaching unity

Photonic generation of microwave pulses with wide frequency multiplication tuning range

In this paper, we propose an approach to generate microwave pulses with wide frequency multiplication tuning range based on the unbalanced temporal pulse shaping (TPS) principle. The key to achieving a wide tuning range is a linearly chirped fiber Bragg grating (LCFBG) with programmable dispersion which is incorporated in an unbalanced TPS system. We experimentally demonstrate generation of microwave pulses whose centre frequency can be tuned from 3.7 GHz to 9.2 GHz

Generation of tunable continuous-wave microwave signals using photonic techniques

This paper reviews two photonic techniques which have been recently proposed and demonstrated by us for generating tunable continuous-wave microwave signals. In general, both techniques are based on the photonic processing of a pulse-train generated by a mode-locked fiber laser

Characterization of the excess noise conversion from optical relative intensity noise in the photodetection of mode-locked lasers for microwave signal synthesis

Excess noise converted from the optical relative intensity noise (RIN) has limited the noise performance in the microwave signal synthesis application for mode-locked lasers. In this paper, a method for detailed characterization of the excess noise conversion from the optical RIN to the electrical pulse width jitter (PWJ), electrical relative amplitude noise (RAN) and electrical phase noise in the photodetection of mode-locked lasers is proposed. With the measured noise conversion ratios, one can predict the electrical RAN and phase noise power spectral densities under different input optical powers. The effect of the pulse width and peak power of the incident optical pulses and the effect of the saturation power of the photodetectors are also investigated. The results are used to suggest guidelines for achieving low-noise photodetection for microwave signal synthesis application.Accepted versio

Noise conversion from pump to the passively mode-locked fiber lasers at 1.5 μm

We characterize the noise conversion from the pump relative intensity noise (RIN) to the RIN and phase noise of passively mode-locked lasers at 1.5 μm. Two mode locking mechanisms, nonlinear polarization rotation (NPR) and semiconductor saturable absorber mirror (SESAM), are compared for noise conversion for the first time. It is found that the RIN and the phase noise of both types of lasers are dominated by the noise converted from the pump RIN and thus, can be predicted with the measured pump RIN and noise conversion ratios. The SESAM laser is found to show an excess noise conversion from the laser RIN to the laser phase noise due to the slow saturable absorber effect.Published versio