Metamorphic InP/InGaAs heterojunction bipolar ... - IEEE Xplore

IEEE TRANSACTIONS ON ELECTRON DEVICES, VOL. 48, NO. 12, DECEMBER 2001

2671

Metamorphic InP/InGaAs Heterojunction Bipolar Transistors on GaAs Substrate: DC and Microwave Performances Hong Wang, Member, IEEE, Geok Ing Ng, Senior Member, IEEE, Haiqun Zheng, Member, IEEE, Hong Yang, Yongzhong Xiong, Member, IEEE, Subratra Halder, Member, IEEE, Kaihua Yuan, Chee Leong Tan, K. Rahdakrishnan, and Soon Fatt Yoon

Abstract—High-performance InP/In0 53 Ga0 47 As metamorphic heterojunction bipolar transistors (MHBTs) on GaAs substrate have been fabricated using In Ga1 P strain relief buffer layer grown by solid-source molecular beam epitaxy (SSMBE). The MHBTs exhibited a dc current gain over 100, a unity current gain cutoff frequency ( ) of 48 GHz and a maximum oscillation frequency ( MAX ) of 42 GHz with low junction leakage current and high breakdown voltages. It has also been shown that the MHBTs have achieved a minimum noise figure of 2 dB at 2 GHz (devices with 5 5 m2 emitter) and a maximum output power of 18 dBm at 2.5 GHz (devices with 5 20 m2 emitter), which are comparable to the values reported on the lattice-matched HBTs (LHBTs). The dc and microwave characteristics show the great potential of the InP/InGaAs MHBTs on GaAs substrate for high-frequency and high-speed applications. Index Terms—GaAs, heterojunction bipolar transistor (HBT), InP/InGaAs, metamorphic, , MAX , microwave noise, microwave power.

I. INTRODUCTION

R

ECENT advances in the metamorphic growth technology—growing InP-based devices on GaAs substrates have resulted in metamorphic high-electron mobility transistors (MHEMTs) with excellent dc and microwave characteristics. The use of metamorphic technology has eliminated the InP substrate related issues such as the limited substrate size, high cost, and brittle nature of the InP material. The great success in metamorphic HEMTs has been the motivation to investigate the fabrication and characterization of performance metamorphic heterojunction bipolar transistors (MHBTs). However, the progress made in realizing high-performance MHBTs has been limited. This is due to a number of factors which include 1) the bipolar transistor structure is much more sensitive to defects than the majority carrier device such as HEMTs; and 2) material growth and device fabrication for InP-based HBTs are more complicate and less mature. Hwang et al. [1] reported a metamorphic InAlAs/InGaAs HBTs on GaAs substrates with a relatively low indium composition (0.33 for InGaAs base). Manuscript received April 16, 2001; revised July 18, 2001. This work was supported by the National Science and Technology Board of Singapore and Defence Science Organization (DSO) of Singapore. The review of this paper was arranged by Editor M.-C. F. Chang. The authors are with the Microelectronics Center, School of Electrical and Electronic Engineering, Nanyang Technological University, Singapore 639798 (e-mail: [email protected]). Publisher Item Identifier S 0018-9383(01)10099-7.

Although using lower indium composition may ease the material growth, it compromises the superior transport properties of InGaAs with higher indium mole faction. Moreover, the high aluminum faction in the emitter may also result potential reliability issues. Therefore, fabrication and characterization of MHBTs with high indium composition which will equal and even surpass the performance of InP-based lattice-matched HBTs (LHBTs) are of great interest. P as stain-relief buffer has been The growth of In Ga studied mainly in the area of growth—where the focus has been relaxation rate and surface roughness control. Growth P instead of conventional InAlAs or InGaAlAs of In Ga for stain-relief buffer provides several advantages. It is more compatible with InP/InGaAs MHBT layers and does not require additional material sources. It may ease the device fabrication P over InGaAs and GaAs. due to the high selectivity of In Ga In this paper, we describe the growth and fabrication of P InP/InGaAs MHBTs on GaAs substrate using In Ga strain-relief buffer. Indium composition of 0.53 which is same as the one for the conventional InP-based HBTs lattice-matched to InP substrate has been achieved. A comprehensive study of the dc, microwave, and high-frequency noise and power characteristics for the MHBTs has been performed. The paper is organized as follows: The growth of MHBT layer structure and fabrication of devices are described in Section II. Detailed dc and microwave characteristics of the MHBTs are presented in Section III. Finally, some conclusions are drawn in Section IV. II. DEVICE STRUCTURE AND FABRICATION The growth of InP/InGaAs MHBT layer was carried out in a Riber 32P MBE system equipped with a Riber KPC250 valved phosphorus (P) cracker cell and a Riber VAC500 valved arsenic (As) cracker cell. Si and Be were used as the n- and p-type dopants, respectively. Prior to growth, oxide desorption was carried out under As GaAs substrates. The oxide desorption temperature was set to 590 C. Growth rates and alloy compositions were calibrated in situ using reflection high-energy electron diffraction (RHEED) intensity oscillation technique and ex situ using high-resolution X-ray diffraction (XRD) rocking curves. Doping concentrations were calibrated by growing a series of Si or Be-doped layers and using Hall measurements to determine their concentrations. The substrate used is a semi-insulating (100) GaAs substrate. The buffer layer consists of a

0018–9383/00$10.00 © 2001 IEEE

2672


Fig. 1. TEM image of In Ga substrate.

P linear graded buffer grown on GaAs

TABLE I LAYER STRUCTURE OF THE METAMORPHIC InP/InGaAs DHBT

Fig. 2. SEM photograph of a fabricated InP HBT with air-bridged interconnections.

air-bridged interconnection process, the issue of mesa step coverage for interconnection metal can be eliminated. Moreover, the use of air-bridged interconnection process allows us to fabricate mesa-type HBTs with small emitter size without using any dielectric layer. This process combined with the nonalloyed TiPtAu ohimc metallization yields a very low thermal budget for the device fabrication. The SEM photograph of a fabricated InP HBT with air-bridged interconnections is given in Fig. 2. Dem to m vices with emitter areas in the range of were fabricated for dc and microwave measurements. III. DEVICE PERFORMANCE AND DISCUSSION A. DC Characteristics 1000- GaAs layer grown at 600 C, a 1.5- m linear grading P ( varying from 0.48 to 1) layer, and a 500- InP In Ga layer grown at 480 C, the temperature used for the rest of the HBT structure is also 480 C. The misfit dislocations in the P buffer were observed in the TEM image shown in In Ga Fig. 1. It can be seen that the misfit dislocations distribute in the P buffer within the range of 600 compositional graded In Ga nm from the InGaP/GaAs interface. Detailed layer structure for the MHBT is given in Table I. The key features of this structure cm include a thin InGaAs base (50 nm) doped at with Be and an InGaAs/InP (350 nm) composite collector with dipole-doped interface. The samples show a crosshatch surface morphology with typical roughness of about 10 nm. The fabrication process for the InP/InGaAs MHBTs is essentially the same as the one for InP/InGaAs LHBTs which we have described in detail in previous publications [2]. The salient feature—air-bridged interconnection, relevant to our MHBTs, is reiterated here. Usually, in order to ensure good isolation for the P grading buffer ( m) MHBTs, an over etching of In Ga is required resulting a much higher mesa height ( 2.1 m) for MHBTs. For such high mesa, the discontinuity of interconnection metal at mesa edge may become an important issue for the MHBTs if the conventional dielectric (SiN or SiO ) isolation and metal interconnection process is applied. Using the

On wafer dc measurements were performed on the devices using a Cascade probe station with a thermal chunk and an HP4156 Semiconductor Parameter Analyzer. Fig. 3 shows the characteristics of a typical MHBT common emitter m . The common-emitter with an emitter size of is higher than 9 V, and base-coloff-state breakdown is about 13.5 V. lector junction breakdown voltage ) characteristics The device shows good current–voltage ( at with low leakage current. The off-state current V is about 75 A. This could be attributed to the low junction leakages (see inset of Fig. 3). In fact, we found that the base-collector (B-C) and base-emitter (B-E) junction leakage current for the MHBTs are only slightly higher than those measured from the LHBTs grown and fabricated using the same facilities and process conditions. The device shows a relatively high output conductance and high offset voltage (0.5 V). Similar results were observed on the referenced LM HBTs, suggesting that the high output conductance and high offset voltage is not due the use of metamorphic structure. The poor output conductance could due to the unoptimized thickness of InGaAs/InP composite collector. It can be improved through the optimization of the design of InGaAs/InP composite collector [3]. The large offset voltage is due to the asymmetry of emitter and collector junction [4]. This can be confirmed by the

WANG et al.: METAMORPHIC InP/InGaAs HBTs ON GaAs SUBSTRATE

2673

2

Fig. 3. Common-emitter characteristics of an MHBT with a 5 10 m emitter. I = 0; 10; 20 . . . 50 A bottom up. Inset: Emitter and collector junction I V characteristics for the same device.

0

Fig. 4. Current gain ( ) versus the collector current for the MHBT at various collector-emitter bias voltages. Inset: Comparison of of the MM HBT to those reported for LHBTs with similar base thickness and doping concentration using different growth techniques.

measurement of the base-emitter and base-collector junction characteristics given in the inset of Fig. 3. versus the collector current Fig. 4 shows the current gain for the MHBT at various collector-emitter bias voltages. The m . As shown, the current gain is over emitter size is 100 when the collector current density is higher than 10 mA. The of the MHBT is close to the values reported for LHBTs with similar base thickness and doping concentration using different growth techniques [5]–[8] (see inset of Fig. 4). To understand the properties of carrier transport in the MHBTs, and further assess the material quality, temperature m device is shown dependence of Gummel plots for a in Fig. 5. At room temperature, the ideality factors for collector and base currents are 1.2 and 1.4, respectively. As the temperature increases, the base-emitter turn-on voltage largely decreases, and the crossover of the base and collector currents remains low. No obvious changes of base and collector ideality factors are observed. To study the carrier transport in the device, collector and base currents in Gummel plots at different temperatures in Fig. 5 V to obtain the values of were extrapolated to and [9]. Activation energy plots for collector and base cur(or ) versus ] are shown in Fig. 6. For rent [

Fig. 5. Temperature dependence of Gummel plots for a 5

2 10 m

device.

Fig. 6. Activation energy plots for collector and base currents extrapolated to V = 0 V [log I (or log I ) versus 1=T ].

the collector current, an of 1.1 eV which is around the sum eV) and the conduction of InGaAs bandgap ( eV), indicates the presence of band discontinuity ( electron injection by thermionic emission. As for the base curof 0.8 eV is obtained which is close to the band gap rent, the of the InGaAs base, indicating that, in this temperature range, the band-to-band recombination plays a dominant role in determining the base current. No trap-related recombination is observed for the base and the collector currents. B. Microwave Characteristics For microwave characteristics, on wafer measurements of -parameters from 1 to 26 GHz using Cascade Microtech Probes and an HP8510 Network Analyzer were used to determine unity and maximum oscillation current gain cutoff frequencies of the devices. Fig. 7(a) shows the current frequencies and the maximum available power gain/maximum gain stable power gain (MAG/MSG) versus frequency for an MHBT m emitter size. The values of and were with and MSG using a obtained by the extrapolation of dB/decade slope. At a collector to emitter bias of 2 V of 3 mA, an of 48 GHz and an and a collector current

2674


Fig. 8. Frequency versus NF and associated gain for an MHBT and an LHBT with 5 5 m emitter measured at I = 1 mA, V = 2 V.

2

j j

Fig. 7. Current gain ( h ) and the maximum available power gain/maximum stable power gain (MAG/MSG) versus frequency for (a) an MM HBT and (b) an LM HBT (emitter size: 5 5 m ). Inset: f and f as the function of emitter current density.

2

of 42 GHz were measured. The values of and as the functions of collector current for the same transistor are shown in Fig. 7(a) as an inset. It should be pointed out that the microwave characteristics measured from the MHBT is lower than those obtained from the referenced LHBT [Fig. 7(b)] grown and fabricated using the same facilities and process conditions. and for the referenced LHBT are 63 The values of GHz and 45 GHz, respectively. This could be explained by the increase of base and collector transit time [10]. C. Microwave Noise and Power Performances To evaluate the high-frequency microwave noise perform emitter were mance of MHBTs, the device with measured using ATN NP5 automated noise measurement system in conjunction with an HP8510B Network Analyzer over 2–14 GHz frequency range. Fig. 8 shows the minimum and associated gain as a function noise figure of frequency. During the measurements, the device was biased mA and V. The increases linearly at at with the increase of frequency. It can be seen that the 2 GHz is about 2 dB for the MHBT, while the referenced LM at 2 GHz at same frequency. HBT shows a 1.4 dB of The values are comparable to the published data on the lattice-matched InP HBTs with similar emitter area and collector current density [11], [12].

Fig. 9. Output power and PAE for (a) an MHBT and (b) an LHBT at 2.5 GHz V = 4 V, I = 2 mA (emitter size: 5 20 m ).

2

Microwave power measurements were carried out using ATN LP1 load-pull system. The devices were driven by a constant voltage source in series with a resistor at the base to facilitate self-biasing current. A resistance of 750 was found to be adequate to deliver high power. The device for power measurements m and is biased for Class AB has an emitter area of operation. The measurement was carried out on unthinned wafer without any heat-sinking mechanism in place. In Fig. 9, the measurements were tuned for maximum power, the MHBT delivered

WANG et al.: METAMORPHIC InP/InGaAs HBTs ON GaAs SUBSTRATE

18 dBm (64 mW) and 40% power-added-efficiency (PAE) at 2.5 V). The LM HBT delivered 20 GHz (bias condition: dBm (100 mW) and 40% PAE at 2.5 GHz under same dc bias condition. When tuned for maximum efficiency, the metamorphic device offered 59% PAE with saturated output power of m 14.5 dBm (30 mW). At frequency of 7.5 GHz, the MHBTs maintains marginally lower power performance of 17 dBm (50 mW) with lower PAE of 23% and small-signal gain of 5 dB. The power performance is expected to increase by thinning the wafer and by providing adequate heat-sinking arrangements. It can also be improved by properly optimizing the device layer structure to further increase the device breakdown voltage and current density. It should be pointed out that the dc and microwave performances which we demonstrate here is based on the devices with relaxed process technology (5 m). With the further optimization the device fabrication technology to reduce the emitter size, better microwave performance for the MHBTs should be expected.

2675

[6] M. Ida, S. Yamahata, K. Kurishima, H. Ito, T. Kobayashi, and Y. in InP/InGaAs HBTs by selective Matsuoka, “Enhancement of f MOCVD growth of heavily-doped extrinsic base regions,” IEEE Trans. Electron Devices, vol. 43, pp. 1812–1818, Sept. 1996. [7] B. Willen, H. Asonen, and M. Toivonen, “InGaAs/lnP heterojunction bipolar transistor grown by all-solid source molecular beam epitaxy,” Electron. Lett., vol. 31, pp. 1514–1515, 1995. [8] J.-I. Song, B. W. P. Hong, C. J. Palmstrom, B. P. Van Der Gaag, and K. B. Chough, “Ultra-high-speed InP/InGaAs heterojunction bipolar transistors,” IEEE Electron Device Lett., vol. 15, pp. 94–96, Apr. 1994. [9] S. Tiwari, S. L. Wright, and A. W. Kleinsasser, “Transport and related properties of (Ga,Al)As/GaAs double heterojunction bipolar transistors,” IEEE Trans. Electron Devices, vol. ED-34, pp. 185–198, Jan. 1987. [10] H. Wang, G. I. Ng, H. Zheng, Y. Z. Xiong, L. H. Chua, K. Yuan, K. Radhakrishnan, and S. F. Yoon, “Demonstration of aluminum-free metamorGa As/InP double heterojunction bipolar transistors phic InP/In on GaAs substrates,” IEEE Electron Device Lett., vol. 21, pp. 379–381, Sept. 2000. [11] V. Danelon, F. Aniel, J. L. Benchimol, J. Mba, M. Riet, P. Crozat, G. Vernet, and R. Adde, “Noise parameters of InP-based double heterojunction base-collector self-aligned bipolar transistors,” IEEE Microwave Guided Wave Lett., vol. 9, no. 5, pp. 195–197, 1999. [12] Y.-K. Chen, R. N. Nottenberg, M. B. Panish, R. A. Hamm, and D. A. Humphrey, “Microwave noise performance of InP/InGaAs heterostructure bipolar transistors,” IEEE Electron Device Lett., vol. 10, pp. 470–472, Oct. 1989.

IV. CONCLUSION In conclusion, we present the first comprehensive characterization of dc and microwave performances for InP/InGaAs metamorphic HBTs. The MHBTs were grown by SSMBE. The fabrication and characterization of InP/InGaAs metamorphic HBTs cm are reported. with a base doping concentration of The device characteristics including dc, RF, microwave noise, and power characteristics have been carefully investigated. The devices exhibit a dc current gain over 100 and a common-emitter larger than 9 V with low junction breakdown voltage of 48 GHz and an of 42 GHz were mealeakages. An m emitter area. Both misured for the devices with crowave noise and power performances for the MHBTs were investigated. A minimum noise figure of 2 dB was obtained on m emitter at frequency of 2 GHz, a maxthe devices with m imum output power of 18 dBm was measured for the devices at frequency of 2.5 GHz. The dc and microwave characteristics demonstrate the great potential of the InP/InGaAs MHBTs on GaAs substrate. We believe that, with the further optimization of material growth and process technologies, devices with better performances, which are suitable for high-frequency and high-speed applications, will be obtained in near future. REFERENCES [1] H.-P. Hwang, J.-L. Shieh, and J.-I. Chyi, “DC and microwave characteristics of In Al As/In Ga As heterojunction bipolar transistors grown on GaAs,” Solid-State Electron., vol. 43, pp. 463–468, 1999. [2] H. Wang and G. I. Ng, “Current transient in polyimide-passivated InP/InGaAs heterojunction bipolar transistors: Systematic experiments and physical model,” IEEE Trans. Electron Devices, vol. 47, pp. 2261–2269, Dec. 2000. [3] , “Avalanche multiplication in InP/InGaAs double heterojunction bipolar transistors with composite collectors,” IEEE Trans. Electron Devices, vol. 47, pp. 1125–1133, June 2000. [4] T. Won, S. Iyer, S. Agarwala, and H. Morkoc, “Collector offset voltage of heterojunction bipolar transistors grown by molecular beam epitaxy,” IEEE Electron Device Lett., vol. 10, pp. 274–276, Aug. 1989. [5] H. Shigematsu, T. Iwai, Y. Matsumiya, H. Ohnishi, O. Ueda, and T. Fujii, “Ultrahigh f and f new self-alignment InP/InGaAs HBTs with a highly Be-doped base layer grown by ALE/MOCVD,” IEEE Electron Device Lett., vol. 16, pp. 55–57, Feb. 1995.

Hong Wang (S’99–M’01) received the B. Eng degree from Zhejiang University, China, in 1998, and the M.Eng. and Ph.D. degrees from Nanyang Technological University (NTU), Singapore, in 1998 and 2001, respectively. From 1988 to 1994, he was with the Institute of Semiconductors, Chinese Academy of Sciences, developing InP-based OEICs. From 1994 to 1995, he was a Royal Research Fellow at British Telecommunications Laboratories, Ipswich, U.K., working on the development of .025- InP-based HFETs using E-beam lithography. In 1996, he joined the Microelectronics Centre at NTU as a Research Associate, where he is currently an Assistant Professor. In 1997, he spent one month at the Institute for Microstructural Sciences, National Research Council, Ottawa, ON, Canada, where he worked on the development of InP HBTs. His current research interests are InP- and GaAsbased compound semiconductor device physics, and fabrication technology and characterization. He has published over 50 technical papers related to his research.

m

Geok Ing Ng (S’84–M’90) received the B.S., M.S., and Ph.D. degrees in electrical engineering from the University of Michigan (UM), Ann Arbor, in 1984, 1986, and 1990, respectively. From 1991 to 1993, he was a Research Fellow at the Centre for Space Terahertz Technology, UM, working on microwave- and millimeter-wave semiconductor devices and MMICs. In 1993, he joined TRW, Inc., Space Park, CA, as Senior Member of Technical Staff engaging in R&D work on GaAs- and InP-based HEMTs for high-frequency, low-noise, and power MMIC applications. In 1994, he joined Nanyang Technological University (NTU), Singapore, where he was a Lecturer in the School of Electrical and Electronic Engineering, and is currently Associate Professor. In 1996, he was appointed Programme Manager for the R&D projects on III-V RF devices and MMICs at the Microelectronics Center at NTU. His current research interests include device physics, and fabrication and characterization of microwave devices with different III-V material systems for low-noise, power, and MMIC applications. Dr. Ng is a member of Tau Beta Pi and Eta Kappa Nu. In 1990, he was awarded the European Microwave Prize for his work on InP-based heterostructure monolithic amplifiers.

2676


Haiqun Zheng (M’98) received the B.Sc. degree in electronic science from Jilin University, Changchun, China, in 1987, and the M.Eng. degree in electrical and electronic engineering from Nanyang Technological University (NTU), Singapore, in 1998. From 1987 to 1995, he was an Engineer in the Institute of Semiconductors, Chinese Academy of Sciences, engaging in the molecular beam epitaxy (MBE) of III-V compound semiconductor structures. From 1996 to 2001, he was a Research Associate at the Microelectronics Centre at NTU, developing phosphorus-containing heterostructures for high-electron mobility transistor (HEMT) and heterojunction bipolar transistor (HBT) applications using solid source MBE (SSMBE). Presently, he is a Principal Engineer with DenseLight Semiconductor Pte Ltd., Singapore, working on the growth and characterization on InP-based laser diode (LD) and HBT structures using metal-organic chemical vapor deposition (MOCVD). His current research interests include MBE and MOCVD growth and characterization of compound semiconductors and their heterostructures for microelectronic and optoelectronic applications and device fabrication and characterization. He is coauthor of more than 100 journal and conference papers. Mr. Zheng is a member of the American Vacuum Society.

Hong Yang received the B.Eng degree from Zhejiang University, China, in 1991, and the M.Eng degree from the Nanyang Technological University (NTU), Singapore, in 1998. From 1991 to 1994, she was with the Institute of Mechanics, Fujian, China. From 1995 to 1996, she was with Seagate Technology International, Singapore. Since 1998, she has been with the Microelectronics Centre at NTU, where she is currently a Research Associate. Her current research interests are InP-based HBT fabrication technology and characterization.

Yongzhong Xiong (M’98) received the B.S. and M.S. degrees in communication and electronic systems from the Nanjing University of Science and Technology (NUST), China, in 1986 and 1990, respectively. He is currently pursuing the Ph.D. degree at Nanyang Technological University (NTU), Singapore. From 1986 to 1992, he was an Engineer at NUST, working on microwave system and ciruit design. In 1992, he became a Lecturer in the Department of Electronic Engineering at NUST. From 1995 to 1997, was with the RF and Radios Department in CEI Technologies Pte. Ltd., Singapore. As a Senior Engineer, he was also attached to the Centre for Wireless Communcations of the National University of Singapore in 1996 to work on the RFIT project. In late 1997, he joined the Microelectronics Centre in NTU as a Research Associate. His major areas of research interest include microwave device modeling, characterization, and MMIC design.

Subratra Halder (M’99) received the B.S. degree from the Indian Institute of Technology, Kharagpur, India, in 1988, and the M.Eng. degree from Nanyang Technological University (NTU), Singapore, in 2001. From 1988 to 1998, he was associated with the Society for Applied Microwave Electronics Engineering and Research, Department of Electronics, Government of India, where he worked on RF receiver subsystem development of large phased array radar system. From October 1999 to March 2001, he was a Project Officer at Microelectronics Division, School of Electrical and Electronic Engineering, NTU, where his research interest was heterostructure device characterization, modeling, and MMIC design. He is currently a Principal Engineer at DenseLight Semiconductor Pte. Ltd, Singapore, where his responsibilities include modeling of active and passive components and high-speed circuit design.

Kaihua Yuan was born in Beijing, China, in 1968. He received the B.S. degree from Peking University, China, in 1991, and the M.S. degree from Beijing University of Aeronautics and Astronautics, China, in 1994. Currently, he is a Research Associate at the Microelectronics Centre, Nanyang Technological University, Singapore. His research interests include MBE material growth, device design, and fabrication and characterization of HEMTs, HBTs, and MMICs.

Chee Leong Tan the B.Eng degree in electrical engineering from the National University of Singapore in 1996. He is currently an Engineer at Defence Science Organization National Laboratories, Singapore. His research interests are in III-V compound semiconductor devices and circuits.

K. Rahdakrishnan (M’01) received the M.Sc. degree in applied physics from University of Madras, India, the M.Tech degree in materials science from Indian Institute of Technology, Kanpur, in 1981, and the Ph.D. degree in physics from National University of Signapore in 1989. In 1991, he joined Nanyang Technological University (NTU), Singapore, as a Research Fellow in the School of Electrical and Electronic Engineering to work on the MBE growth of compound semiconductor materials, where he is now an Associate Professor. His current research includes MBE growth of GaAs and InP-based heterostructures, device physics, passive components, and fabrication and characterization of microwave integrated devices and circuits.

Soon Fatt Yoon is currently Associate Professor in the School of Electrical and Electronic Engineering, Nanyang Technological University (NTU), Singapore, where he holds an appointment as Vice-Dean (Research). He has extensive practical and research experience in the field of thin films, semiconductors, and microelectronic and optoelectronic devices. He has published extensively in these fields. Prof. Yoon is a Member of the International Advisory Committee of a number of international conferences in semiconductor materials, physics, and microelectronic devices. He is also a reviewer for a number of international journals in semiconductor growth using molecular beam epitaxy, low-dimensional heterostructures, high-frequency devices, VLSI-optoelectronic integration, large bandgap semiconductors, diamond-like-carbon films, carbon nanotubes, and technology management in silicon wafer fabrication.