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Fundamental and Dynamic Properties of Intermixed InGaAs-InGaAsP Quantum-Well Lasers Cheng Chen, Student Member, IEEE, Hery Susanto Djie, Member, IEEE, Yun Hsiang Ding, Boon Siew Ooi, Senior Member, IEEE, James C. M. Hwang, Fellow, IEEE, and Vincent Aimez, Member, IEEE
Abstract—The fundamental and dynamic properties of InGaAs-InGaAsP lasers, where emission wavelengths were blueshifted by quantum-well intermixing through ion implantation and annealing, were investigated to assess possible degradation by intermixing. It was found that the fundamental properties such as threshold current and slope efficiency were largely unchanged even after as much as 120 nm of wavelength shift. Meanwhile, the dynamic properties such as modulation efficiency and K factor were degraded after just a moderate degree of intermixing, but the degradation was not worsened by further intermixing. Provided the finite degradation of dynamic properties is tolerable, the present intermixing technique will be very useful for the fabrication of photonic integrated circuits. Index Terms—Dynamic response, gain measurement, ion implantation, optical modulation, quantum wells, semiconductor lasers.
I. Introduction UANTUM-WELL intermixing is a promising technique for the fabrication of photonic integrated circuits [1]–[3]. For example, through ion implantation and annealing under a gray mask, the quantum wells of an array of lasers on the same InP chip can undergo different degrees of intermixing thereby emitting at different wavelengths by design [4], [5]. However, questions remain whether or not such intermixing would degrade the quality of the lasers. Although emission efficiency [6] and carrier capture efficiency [7] have been shown experimentally to benefit from annealing, gain and α factors have been predicted theoretically to vary with intermixing [8]–[11]. Since most investigations to date were limited to either material characteristics [6], [7], [12] or fundamental laser properties [4], [13], [14], it is critical to systematically
investigate the dynamic properties of intermixed quantum-well lasers. In this paper, we report both fundamental and dynamic properties of InGaAs-InGaAsP quantum-well lasers after different degrees of intermixing through low-energy phosphorous ion implantation in conjunction with a gray mask [5], [15]. Specifically, light-current characteristics, amplified spontaneous emission, and intrinsic frequency response were measured to extract critical parameters such as internal quantum efficiency, α factor, effective differential gain, gain compression factor, and effective carrier lifetime. The results showed that while threshold current and slope efficiency were largely unchanged even after as much as 120 nm of blue shift, modulation efficiency and K factor were degraded after just a moderate degree of intermixing. These experimental techniques are discussed next.
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Manuscript received February 18, 2010; revised March 28, 2010; accepted April 4, 2010. Date of current version July 23, 2010. This work was supported in part by the U.S. National Science Foundation, under Grant 0725647US, and the U.S. Army Research Laboratory, under Cooperative Agreement No. W911NF-07-2-0064. This paper was recommended by Associate Editor L. J. Mawst. C. Chen, Y. H. Ding, and J. C. M. Hwang are with Lehigh University, Bethlehem, PA 18015 USA (e-mail:
[email protected];
[email protected];
[email protected]). H. S. Djie is with JDS Uniphase Corporation, San Jose, CA 95134 USA (e-mail:
[email protected]). B. S. Ooi is with King Abdullah University of Science and Technology, Jeddah 21534, Saudi Arabia (e-mail:
[email protected]). V. Aimez is with the Center de Recherche en Nanofabrication et en Nanocaractérisation, University of Sherbrooke, Sherbrooke, QC J1K 2R1, Canada (e-mail:
[email protected]). Color versions of one or more of the figures in this paper are available online at http://ieeexplore.ieee.org. Digital Object Identifier 10.1109/JQE.2010.2047939
II. Experimental A. Laser Design and Fabrication Details of the laser design and fabrication have been reported elsewhere [2]. Briefly, a separate-confinement InGaAsInGaAsP heterostructure was grown lattice-matched by metalorganic chemical vapor deposition on a Si-doped (100) InP substrate. As illustrated in Fig. 1, the undoped active region consists of five 5.5-nm-thick In0.53 Ga0.47 As wells, which are separated by 12-nm-thick In0.76 Ga0.24 As0.53 P0.47 barriers. Optical confinement is provided first by 50-nmthick In0.81 Ga0.19 As0.42 P0.58 layers, then by 80-nm-thick In0.90 Ga0.10 As0.23 P0.77 layers. The upper cladding is a 1.5-μm-thick InP layer doped with 7 × 1017 cm−3 of Zn, while the lower cladding is a 1.0-μm-thick InP layer doped with 3 × 1018 cm−3 of Si. At room temperature, the as-grown heterostructure gives a photoluminescence peak at 1570 nm. For intermixing, the heterostructure was capped with a SiO2 gray mask before undergoing ion implantation and annealing. Across the gray mask, the SiO2 thickness was stepped from 0 to 200 nm, 350 nm, 540 nm and 1000 nm by plasmaenhanced chemical vapor deposition. The ion implantation involved 5 × 1014 cm−2 of phosphorous ions at 360 keV. The annealing was performed at 725 °C for 120 s. The simulated [16] phosphorous profile is overlaid on Fig. 1. It can be seen that different SiO2 thicknesses resulted in different amount of phosphorous in the heterostructure, except in the case of the 1000-nm-thick SiO2 , which was too thick for any phosphorous
c 2010 IEEE 0018-9197/$26.00
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Fig. 1. Conduction band energy of the quantum-well heterostructure and depth profile of phosphorous ions implanted through SiO2 masks 0, 200 nm, 350 nm, 540 nm, and 1000 nm thick.
to penetrate. Further, most of the phosphorous that reached the heterostructure stopped in the InP cladding short of the InGaAs quantum wells. This confirms that instead of directly damaging the quantum wells, the low-energy phosphorous implantation increased the vacancy concentration near the surface, which then indiffused to the quantum wells to cause intermixing there [17]. After intermixing, the heterostructure was fabricated into lasers with a 3 μm-wide ridge and a 400-μm-long cavity without facet coating. For internal loss and efficiency measurements, additional lasers were made with cavity lengths of 700, 1000, 1500, and 2000 μm. B. Laser Characterization Bare laser dies were characterized at 20 °C in a probe station equipped with a thermoelectric chuck. Self heating was minimized by using pulsed biases with low duty cycles. Most measurements were performed with 5 μs pulses at 5% duty cycle, except amplified spontaneous emission was measured with 1 μs pulses at 1% duty cycle. Emission spectra were measured by an optical spectrum analyzer, which was coupled to the laser through a lensed single-mode fiber with a 9-μmdiameter core. For each type of laser, several devices were measured repeatedly over a course of several months to ensure the results were reproducible and representative. From the amplified spontaneous emission, net modal gain G was extracted by using the Hakki-Paoli method [18]. Based on the dependence of the net modal gain on the bias current, the bias dependence of modal gain dG/dI was determined. From the bias dependence of the Fabry-Perot resonance peaks, the bias dependence of the refractive index dn/dI was also determined, which was then used to calculate the α factor [19]. Instead of electrical injection modulation, optical injection modulation was used to reveal intrinsic dynamic properties without parasitic resistances and capacitances [20]. Using a custom setup [21], both the electrical bias and the optical injection were pulsed. The pulsed optical injection is in turn modulated by a LiNbO3 Mach-Zehnder modulator, which is driven by the amplified signal of a microwave network analyzer between 0.5 and 8 GHz. The optical injection is at 1310 nm with the photon energy higher than the bandgap of
Fig. 2. (a) Emission wavelength λG of intermixed lasers decreases with decreasing SiO2 thickness while threshold current ITH remains approximately constant. (b) Internal quantum efficiency ηI and internal loss αI both decrease linearly with decreasing SiO2 thickness, leaving slope efficiency ESLOPE approximately constant.
the In0.53 Ga0.47 As wells but lower than the bandgap of the In0.76 Ga0.24 As0.53 P0.47 barriers [22].
III. Results and Discussion A. Fundamental Properties Fig. 2(a) shows the threshold currents and emission wavelengths of lasers intermixed under different thicknesses of SiO2 . It can be seen that while the threshold varies little, the wavelength decreases with decreasing SiO2 thickness reflecting increasing degree of intermixing. However, the blue shift appears to saturate when the SiO2 is thinner than 200 nm. By contrast, the laser with 1000 nm SiO2 emits at 1565 nm, which is very close to the photoluminescence peak of the as-grown heterostructure. This confirms that without the phosphorous ions, the effect of thermal-annealing-induced intermixing is negligible. Therefore, in this paper, the lasers with 0 and 1000 nm SiO2 are referred to as “fully intermixed” and “unintermixed,” respectively. Photoluminescence spectra of all lasers intermixed under different thicknesses of SiO2 show no discernable change after intermixing [15]. Fig. 2(b) shows that the internal quantum efficiency ηI and the internal loss αI both decrease approximately linearly with decreasing SiO2 thickness, leaving the slope efficiency ESLOPE approximately constant. Here ηI and αI are extracted from
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the relationship between slope efficiency and cavity length [23]. The decrease of ηI after intermixing is probably due to increased carrier leakage from more graded quantum wells. The decrease of αI after intermixing is probably due to less carrier absorption or better optical confinement at shorter wavelengths. The decrease of αI is comparable in magnitude to that reported for intermixed InGaAs-GaAs and InGaAsInGaAsP lasers [13], [24]. Fig. 3 shows that compared to the un-intermixed laser, the intermixed lasers have comparable but more bias-dependent gains. Fig. 3(a) plots the gain spectra measured approximately 10% below threshold. All five lasers have similar peak gains, but the intermixed lasers appear to be more narrowband than the un-intermixed laser. However, considering the blue shifts of the intermixed lasers, the bandwidths are actually similar in terms of energy. Fig. 3(b) and (c) shows that the net modal gain and Fabry-Perot peak shift, respectively, at the lasing wavelength of the intermixed lasers are more biasdependent than that of the un-intermixed laser. Furthermore, Fig. 4(a) and (b) shows that at all wavelengths around the gain peak, the bias sensitivities of the net modal gain and the refractive index of the lasers with 0–350 nm SiO2 are approximately twice that of the lasers with 540 nm and 1000 nm SiO2 . Such an abrupt dependence on the SiO2 thickness is qualitatively different from the linear dependence of the internal loss and internal quantum efficiency shown in Fig. 2(b), which suggests different mechanisms. Assuming the internal loss is independent of bias, the bias dependence of the net model gain and the refractive index can be expressed as dG dI = d(g − αI ) dI = dg dN dN dI
(1)
dn dI = dn dN dN dI
(2)
where is the optical confinement factor, g is the material gain, and N is the carrier concentration in the active region. Our simulation shows that with intermixing-induced blue shift, should increase only slightly while dg/dN should decrease (Section III-B). Therefore, the abrupt increase in dG/dI and dn/dI is likely caused by an increase in dN/dI. This implies that the subband structure changes substantially only after a certain degree of intermixing, which changes not only the grading of the well boundary, but also the overall shape of the quantum well. Due to the compensating effects of dG/dI and dn/dI on the α factor, Fig. 4(c) shows that the α factor decreases only slightly with intermixing. Fig. 5 illustrates the relatively constant α factor in contrast to the abrupt changes of dG/dI and dn/dI with the blue shift. This implies that the intermixed subband structure and carrier population may have more symmetric gain spectra and less chirp under direct modulation. B. Dynamic Properties Fig. 6 compares the intrinsic frequency response under different biases of the fully intermixed laser with that of the un-intermixed laser. It can be seen that after intermixing, relaxation oscillations occur at lower frequencies. The measured
Fig. 3. (a) Gain spectra measured 10% below threshold on the intermixed lasers are comparable to that of the un-intermixed laser. However, (b) net modal gains and (c) Fabry-Perot peak shifts at the lasing wavelength of the intermixed lasers are more bias-dependent.
frequency response can be fitted to the following expression [23] to extract the relaxation frequency fR and the damping factor γ (3) MI = fR2 fR2 − f 2 + jfγ 2π . Fig. 7 shows that the extracted relaxation frequency exhibits a square-law dependence on both the net injection current I − ITH and the damping factor. However, intermixing decreases the relaxation frequency and increases damping, implying reduced modulation efficiency EM . The relationship between
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Fig. 6. Intrinsic frequency response measured under different net injection current I − ITH on (a) fully intermixed laser, which exhibits lower frequency relaxation oscillation than that of (b) un-intermixed laser.
the relaxation frequency and the net injection current can be used to extract the modulation efficiency; the relationship between the relaxation frequency and the damping factor can be used to extract the K factor and the effective carrier lifetime τEFF [25] γ = KfR2 + 1 τEFF . (4)
Fig. 4. Bias dependence of (a) net modal gain dG/dI, (b) bias dependence of refractive index |dn/dI|, and (c) α factor as functions of wavelength for lasers with different degrees of intermixing.
Fig. 8(a) shows that intermixing increases the K factor while decreasing the modulation efficiency, but the amount of increase or decrease is not a sensitive function of the degree of intermixing. The K factor is critical to the microwave modulation bandwidth. After intermixing, the K factor increases from 0.39 ns to 0.49 ns, so that the intrinsic modulation bandwidth decreases from 23 GHz to 18 GHz. In turn, the K factor can be used to extract the gain compression factor ε according to (5) K = 4π2 τp + ε vG a where τP ≈ 3 ps is the photon lifetime, vG is the group velocity, and a is the effective differential gain. The effective differential gain can be calculated from the modulation efficiency and slope efficiency [26] 2 vG ESLOPE a = 4π2 αM (αM + αI ) VACT hνEM
Fig. 5. Bias dependence of the net modal gain dG/dI and the refractive index |dn/dI| showing abrupt increases with increasing wavelength shift, while the α factor decreases only slightly.
(6)
where αM is the mirror loss, αI is the internal loss, hν is the photon energy, and VACT is the active volume.
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Fig. 7. Extracted relaxation frequency fR 2 versus (a) net injection current I − ITH and (b) damping factor γ. Intermixing decreases relaxation frequency abruptly but increases damping only slightly.
Fig. 8(b) shows that while the gain compression factor and the effective carrier lifetime improve after intermixing, the effective differential gain degrades. Again, the amount of degradation is independent of the degree of intermixing. According to (5), the K factor is proportional to the ratio of ε/a . Thus, although both ε and a decrease after intermixing, the decrease in a is more pronounced, which results in a higher K. Typically, the effective differential gain can be expressed as [25] a = 1 χ dg dN (7) where χ is the transport factor, and χ = 1 + τC τE
(8)
where τC and τE are carrier capture and escape times, respectively. While carrier capture depends on the overall shape of the quantum well, carrier escape depends mainly on the grading of the well boundary. With a moderate degree of intermixing, the well boundary becomes more graded but the overall well shape does not change significantly, so τE decreases more than τC does, resulting in a larger χ and a smaller a . With further intermixing, τC and τE probably decrease proportionally so that χ does not increase further. Gain compression is supposed to decrease as intermixing relaxes quantum confinement and tightens subband structure.
Fig. 8. Extracted dependence on intermixing-induced wavelength shift of (a) K factor and modulation efficiency EM and (b) effective differential gain a , gain compression factor ε, effective carrier lifetime τEFF , and the product a τEFF .
Since the gain compression factor is observed to change only slightly in Fig. 8(b), this effect does not appear to be very strong. The effective carrier lifetime is related to χ by the carrier recombination lifetime τN [25] τEFF = χτN .
(9)
While a larger χ can certainly lead to a larger τEFF , τN is also expected to increase after intermixing, because carrier recombination is dominated by Auger recombination [27], which would decrease with increasing bandgap [28]. The transport factor χ is canceled out in the product of a and τEFF a τEFF = τN dg dN. (10) Fig. 8(b) shows that a τEFF changes little with intermixing. Since τN increases with intermixing, dg/dN can only decrease with intermixing. This property of dg/dN was used in (1) to argue for the increase of dN/dI after intermixing. The degradation of dynamic properties after intermixing may be mitigated by replacing InGaAsP barriers with the InGaAlAs barriers. InGaAlAs barriers would provide a higher conduction band offset and better carrier confinement, so that the carrier escape time would remain long after intermixing. More quantum wells could also enhance carrier confinement but care must be taken to maintain uniform carrier concentration and separate confinement. While dopant diffusion from
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the cladding may reduce τC , it may also offset the decrease in τE , thus keeping χ more constant. In this case, the width of separate confinement needs to be optimized to avoid significant increases in internal loss and threshold.
IV. Conclusion It was found that the fundamental properties such as threshold current and slope efficiency of InGaAs-InGaAsP quantumwell lasers were largely unchanged even after as much as 120 nm of blue shift. Meanwhile, the dynamic properties such as modulation efficiency and bandwidth were degraded after just a moderate degree of intermixing. However, the degradation was approximately 25% and it was not worsened by further intermixing. Provided the finite degradation of dynamic properties is tolerable, the present intermixing technique will be very useful for the fabrication of photonic integrated circuits.
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[13] Y.-R. Zhao, G. A. Smolyakov, and M. Osinski, “High-performance InGaAs-GaAs-AlGaAs broad-area diode lasers with impurity-free intermixed active region,” IEEE J. Sel. Top. Quantum Electron., vol. 9, no. 5, pp. 1333–1339, Sep.–Oct. 2003. [14] S. Burkner, J. D. Ralston, S. Weisser, J. Rosenzweig, E. C. Larkins, R. E. Sah, and J. Fleissner, “Wavelength tuning of high-speed InGaAs-GaAsAlGaAs pseudomorphic MQW lasers via impurity-free interdiffusion,” IEEE Photon. Technol. Lett., vol. 7, no. 9, pp. 941–943, Sep. 1995. [15] S. L. Ng, H. S. Lim, Y. L. Lam, Y. C. Chan, B. S. Ooi, V. Aimez, J. Beauvais, and J. Beerens, “Generation of multiple energy bandgaps using a gray mask process and quantum well intermixing,” Jpn. J. Appl. Phys., vol. 41, pp. 1080–1084, Feb. 2002. [16] The Stopping and Range of Ions in Matter [Online]. Available: http://www.srim.org/ [17] H. S. Djie, O. Gunawan, D.-N. Wang, B. S. Ooi, and J. C. M. Hwang, “Group-III vacancy induced Inx Ga1−x As quantum dot interdiffusion,” Phys. Rev. B, vol. 73, pp. 1553241-1–1553241-6, May 2006. [18] B. W. Hakki and T. L. Paoli, “Gain spectra in GaAs doubleheterostructure injection lasers,” J. Appl. Phys., vol. 46, pp. 1299–1306, Mar. 1975. [19] M. Osinski and J. Buus, “Linewidth broadening factor in semiconductorlasers: An overview,” IEEE J. Quantum Electron., vol. 23, no. 1, pp. 9–29, Jan. 1987. [20] C. B. Su, J. Eom, C. H. Lange, C. B. Kim, R. B. Lauer, W. C. Rideout, and J. S. Lacourse, “Characterization of the dynamics of semiconductorlasers using optical modulation,” IEEE J. Quantum Electron., vol. 28, no. 1, pp. 118–127, Jan. 1992. [21] C. Chen, S. Halder, B. S. Ooi, and J. C. M. Hwang, “Intrinsic response of quantum dash lasers under optical modulation,” in Proc. Annu. Meet. IEEE Lasers Electro-Opt. Soc., Nov. 2008, pp. 471–472. [22] D. Vassilovski, T. C. Wu, S. Kan, K. Y. Lau, and C. E. Zah, “Unambiguous determination of quantum capture, carrier diffusion, and intrinsic effects in quantum-well laser dynamics using wavelengthselective optical modulation,” IEEE Photon. Technol. Lett., vol. 7, no. 7, pp. 706–708, Jul. 1995. [23] L. A. Coldren and S. W. Corzin, Diode Lasers and Photonic Integrated Circuits. New York: Wiley, 1995. [24] A. McKee, C. J. McLean, A. C. Bryce, R. M. D. L. Rue, J. H. Marsh, and C. Button, “High quality wavelength tuned multiquantum well GaInAs/GaInAsP lasers fabricated using photoabsorption induced disordering,” Appl. Phys. Lett., vol. 65, no. 18, pp. 2263–2265, Oct. 1994. [25] R. Nagarajan, M. Ishikawa, T. Fukushima, R. S. Geels, and J. E. Bowers, “High-speed quantum-well lasers and carrier transport effects,” IEEE J. Quantum Electron., vol. 28, no. 10, pp. 1990–2008, Oct. 1992. [26] Y. Matsui, H. Murai, S. Arahira, Y. Ogawa, and A. Suzuki, “Enhanced modulation bandwidth for strain-compensated InGaAlAsInGaAsP MQW lasers,” IEEE J. Quantum Electron., vol. 34, no. 10, pp. 1970–1978, Oct. 1998. [27] T. Keating, X. Jin, S. L. Chuang, and K. Hess, “Temperature dependence of electrical and optical modulation responses of quantum-well lasers,” IEEE J. Quantum Electron., vol. 35, no. 10, pp. 1526–1534, Oct. 1999. [28] S. J. Sweeney, A. F. Phillips, A. R. Adams, E. P. O’Reilly, and P. J. A. Thijs, “The effect of temperature dependent processes on the performance of 1.5 μm compressively strained InGaAs(P) MQW semiconductor diode lasers,” IEEE Photonic Technol. Lett., vol. 10, no. 8, pp. 1076–1078, Aug. 1998.
Cheng Chen (S’06) received the B.S. degree in physics from Wuhan University, Wuhan, China, in 2002, and the M.S. degree in electrical engineering from the Chinese Academy of Sciences, Beijing, China, in 2005. He is currently pursuing the Ph.D. degree in electrical and computer engineering from Lehigh University, Bethlehem, PA. He is currently with RF Micro Devices, Inc., Greensboro, NC, where he is responsible for the development of pseudomorphic high electron mobility transistor-based radio frequency switches. His current research interests include characterization and modeling of quantumdash lasers, novel transmission-line structures, and GaAs-based heterojunction bipolar transistors.
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Hery Susanto Djie (S’00–M’04) received the B.Eng (First Class Honors) degree in electrical engineering from Pelita Harapan University, Indonesia, in 1999, under the Lippo Group Scholarship, and the Ph.D. degree from the Electrical Engineering Department, Nanyang Technological University, Singapore, in 2004. He later joined Agilent Technologies, Singapore, where he was in charge of the development of highbrightness light-emitting diodes. From 2004 to 2007, he was a Research Scientist with the Center for Optical Technologies, Lehigh University, Bethlehem, PA, where he was a key contributor in the technology and development of quantum-dot bandgap engineering and semiconductor broadband emitter. Since 2007, he has been a Development Engineer with JDS Uniphase Corporation, San Jose, CA, for high-volume manufacturing of high power laser diode, high-speed semiconductor laser, widely tunable semiconductor laser, optical add-drop multiplexer, and photonic integrated circuits. He has published over 180 international technical papers and has several U.S. patents pending in the field of monolithic integration of photonic devices, quantum-dot and quantum-well intermixing, semiconductor laser, and broadband semiconductor light source. Dr. Djie is a member of the International Society for Optical Engineers, the Materials Research Society, and the Sigma Xi Scientific Research Society.
Yun Hsiang Ding received the B.S. degree in electrophysics from National Chiao Tung University, Hsinchu, Taiwan, in 2000, and the M.S. degree in electrical engineering from George Washington University, Washington D.C., in 2005. She is currently pursuing the Ph.D. degree in electrical engineering from Lehigh University, Bethlehem, PA. From 2000 to 2002, she was a Full-Time Teaching Assistant with National Chiao Tung University. Her current research interests include fabrication and characterization of high-power semiconductor lasers, quantum well, and quantum dash intermixing process. Ms. Ding has been an Officer of the International Society for Optical Engineering, Lehigh Student Chapter since 2006.
Boon S. Ooi (M’95–SM’03) received the B.Eng. and Ph.D. degrees in electronics and electrical engineering from the University of Glasgow, Glasgow, U.K., in 1992 and 1994, respectively. From 1996 to 2000, he was an Assistant Professor with Nanyang Technological University, Singapore. He was a Vice President with Phosistor Technologies, Inc., Pleasanton, CA, from 2000 to 2003. From 2003 to 2009, he was an Associate Professor with Lehigh University, Bethlehem, PA. He is currently the Founding Full Professor of Electrical Engineer-
ing with the King Abdullah University of Science and Technology, Jeddah, Saudi Arabia. He has authored or co-authored of over 200 technical papers. His current research interests include primarily the development of monolithic integration processes for semiconductor photonic integrated circuits using quantum-well/dot intermixing, and the development of semiconductor quantum-dot or dash based broadband emitters for communications, sensing and imaging applications. Dr. Ooi is a Fellow of the International Society for Optical Engineers and the Institute of Physics.
James C. M. Hwang (M’81–SM’82–F’94) received the B.S. degree in physics from National Taiwan University, Taipei, Taiwan, in 1970, and the M.S. and Ph.D. degrees in materials science from Cornell University, Ithaca, NY, in 1976 and 1978, respectively. After working with IBM, Armonk, NY, AT&T, Inc., Dallas, TX, GE, Fairfield, CT, and GAIN, Geneva, Switzerland, he joined Lehigh University, Bethlehem, PA, in 1988. He has authored or coauthored over 200 technical papers. He holds four U.S. patents. His current research interests include micro-electro-mechanical systems, microwave transistors and integrated circuits, lasers, and photodetectors. Dr. Hwang was the recipient of the 2007 IBM Faculty Award.
Vincent Aimez (S’98–M’00) received the B.S. degree in applied physics with microelectronics and computing from the University of Kingston, Kingston, U.K., in 1996, and the M.S. and Ph.D. degrees in electrical engineering from the Université de Sherbrooke, Sherbrooke, QC, Canada, in 1998 and 2000, respectively. His work involved quantum well intermixing using low energy ion implantation for optoelectronic device integration. In 2000, he was an Assistant Professor with the Department of Electrical Engineering, Université de Sherbrooke. He is currently a Full Professor and the Head of the Center de Recherche en Nanofabrication et en Nanocaractérisation, Université de Sherbrooke, and created the Center National de la Récherche Scientifique International Laboratory on Nanotechnology and Nanosystems, Department of Electrical and Computer Engineering, Faculty of Engineering, Université de Sherbrooke, Sherbrooke, Québec, Canada, in 2008. He has authored or co-authored over 150 journal and conference papers. His current research interests include nanophotonic/optoelectronic devices based on silicon, InP, GaAs, and GaN heterostructures for telecom, biophotonic, solid state lighting, and concentrated photovoltaic applications.
