IEEE JOURNAL OF SELECTED TOPICS IN QUANTUM ELECTRONICS, VOL. 17, NO. 5, SEPTEMBER/OCTOBER 2011 1175 Lateral-Current-Injection Distributed Feedback Laser With Surface Grating Structure Takahiko Shindo, Student Member, IEEE, Tadashi Okumura, Member, IEEE, Hitomi Ito, Takayuki Koguchi, Daisuke Takahashi, Student Member, IEEE, Yuki Atsumi, Student Member, IEEE, Joonhyun Kang, Ryo Osabe, Tomohiro Amemiya, Member, IEEE, Nobuhiko Nishiyama, Senior Member, IEEE, and Shigehisa Arai, Fellow, IEEE Abstract—As a step toward the realization of injection-type membrane distributed feedback (DFB) lasers, which are expected to be important components of optical interconnections, we re- alized lateral-current-injection DFB (LCI-DFB) lasers with sur- face grating structures prepared on semiinsulating InP substrates. First, we designed the surface grating structure to have a high index-coupling coefficient together with a high optical confinement in the quantum wells. Then, we investigated the surface grating structure formed on an amorphous-Si (a-Si) layer deposited on the GaInAsP/InP initial wafer containing five quantum wells. A mod- erately low threshold current of 7.0 mA and a high differential quantum efficiency of 43% from the front facet were obtained un- der a continuous-wave operating condition at room temperature for a uniform grating LCI-DFB laser with a stripe width of 2.0 μm and a cavity length of 300 μm. A threshold current of 5.8 mA was obtained with a λ/4 phase-shifted LCI-DFB laser with a-Si sur- face grating. Furthermore, a small-signal modulation bandwidth of 4.8 GHz was obtained at a bias current of 30 mA with a modu- lation current efficiency factor of 1.0 GHz/mA 1 /2 . Index Terms—Lateral-current-injection (LCI), membrane laser, organometallic vapor phase epitaxy (OMVPE) regrowth. I. INTRODUCTION T HE progress in the processing speed and integration of large-scale integrated circuits (LSI) has obeyed Moore’s law. However, as scaling advances, this progress will soon con- front limitations associated with RC delay or ohmic heating in Manuscript received December 1, 2010; revised January 31, 2011 and March 7, 2011; accepted March 10, 2011. Date of publication May 16, 2011; date of current version October 5, 2011. This work was supported in part by the Grants-in-Aid for Scientific Research from the Ministry of Education, Culture, Sports, Science, and Technology (MEXT), Japan, under Grant #19002009, Grant #22360138, Grant #21226010, Grant #08J55211, Grant #10J08973 and Grant #196860230, and in part by the Japan Society for the Promotion of Science (JSPS) FIRST Program. The work of T. Okumura was also supported by the Japan Society for the Promotion of Science (JSPS) for the Research Fellowship for Young Scientists. T. Shindo, T. Okumura, H. Ito, T. Koguchi, D. Takahashi, Y. Atsumi, J. Kang, R. Osabe, T. Amemiya, and N. Nishiyama are with the Department of Electrical and Electronic Engineering, Tokyo Institute of Technology, Meguro-ku, Tokyo 152–8552, Japan (e-mail: shindou.t.aa@m.titech.ac.jp; tokumura@quantum.pe.titech.ac.jp; ito.h.ae@m.titech.ac.jp; koguchi.t.aa@ m.titech.ac.jp; takahashi.d.aa@m.titech.ac.jp; atsumi.y.ab@m.titech.ac.jp; kang.j.aa@m.titech.ac.jp; osabe.r.aa@m.titech.ac.jp; amemiya.t.ab@m.titech. ac.jp; n-nishi@pe.titech.ac.jp). S. Arai is with the Department of Electrical and Electronic Engineering and the Quantum Nanoelectronics Research Center, Tokyo Institute of Technology, Meguro-ku, Tokyo 152-8552, Japan (e-mail: arai@pe.titech.ac.jp). 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/JSTQE.2011.2131636 the electrical interconnections [1], [2]. This is especially true in global wiring, which involves relatively long-distance in- terconnections in the LSI; the signal-delay or the large-power dissipation will limit the performance of the LSI. Consequently, various approaches for solving these problems have been ex- tensively studied [3]. One of the promising approaches is re- placing the global wiring in the LSI with optical interconnec- tions [4]–[6]. Optical communication played a key role in the long-distance fiber communication technology of past decades, but it is now being introduced to applications involving short- distance transmission (e.g., the explosive spread of FTTH or the introduction of optical interconnections to large-scale server systems). As a replacement for electrical wiring, optical inter- connections are being extensively studied for board-to-board, chip-to-chip, and on-chip interconnections. Optical signal trans- mission has an advantage in terms of signal delay because it is independent of the wiring capacity. In addition, high-speed and wideband data transmission is expected from the wavelength division multiplexing technique [7]. The power dissipation of optical devices for on-chip interconnections should be much lower than that of the conventional optical components used for long-haul transmissions. For example, the available power dissipation of modulating the signal is estimated by Miller to be less than 100 fJ/bit [8]. If we want to use directly modu- lated semiconductor lasers, this simply means that the available injection current is limited to 1 mA when the driving voltage and modulated speed of the semiconductor laser are 1 V and 10 Gb/s, respectively. Therefore, an ultralow power consump- tion semiconductor light source will be a key device for on-chip optical interconnection systems. Microdisk lasers [9] or photonic crystal lasers [10]–[12] have been reported to be promising devices for ultralow threshold op- eration because of their strong optical confinement structures; however, they have several disadvantages, such as low-output efficiency and high electrical resistance. Alternatively, we pro- posed a semiconductor membrane laser that utilizes a high-index contrast waveguide structure in the vertical direction. In the conventional laser structure, which has semiconductor cladding layers, the refractive index difference between the core region and the cladding region is about 5%, while an optical confine- ment factor of 1% per quantum well can be obtained from this structure. On the other hand, the proposed membrane struc- ture consists of low-refractive index-material cladding layers, such as SiO 2 instead of a semiconductor. The membrane struc- ture exhibits a large-refractive index difference—up to 40%— between the core region and the cladding region. 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