Shigeo Tamura

High-performance 1.55-/spl mu/m wavelength GaInAsP-InP distributed-feedback lasers with wirelike active regions

High-performance 1.55-/spl mu/m wavelength GaInAsP-InP strongly index-coupled and gain-matched distributed-feedback (DFB) lasers with periodic wirelike active regions mere fabricated by electron beam lithography, CH/sub 4//H/sub 2/-reactive ion etching, and organometallic vapor-phase epitaxial regrowth, whose index-coupling coefficient was more than 300 cm/sup -1/. In order to design lasers for low threshold current operation, threshold current dependences on the number of quantum wells and the wire width mere investigated both theoretically and experimentally. A record low threshold current density of 94 A/cm/sup 2/ among 1.55-/spl mu/m DFB lasers was successfully obtained for a stripe width of 19.5 /spl mu/m and a cavity length of 600 /spl mu/m. Moreover, a record low threshold current of 0.7 mA was also realized at room temperature under CW condition for a 2.3-/spl mu/m-wide buried heterostructure with a 200-/spl mu/m-long cavity. Finally, we confirmed stable single-mode operation due to a gain-matching effect between the standing-wave profile and the wirelike active region.

Optically pumped membrane BH-DFB lasers for low-threshold and single-mode operation

High optical confinement and high index coupling in 1.55 /spl mu/m-wavelength GaInAsP-InP membrane buried heterostructure distributed feedback (BH-DFB) lasers consisting of deeply etched single-quantum-well wire-like active regions were demonstrated under room-temperature (RT) continuous-wave (CW) optical pumping. A threshold pump power of 1.5 mW and a submode suppression ratio (SMSR) of 42 dB were obtained for a 142-nm-thick membrane with a cavity length of 120 /spl mu/m and a stripe width of 2 /spl mu/m. We have also realized membrane BH-DFB laser arrays by arranging the laser cavities (10 /spl mu/m spaced 15 elements with five different grating periods). A total wavelength span of 72 nm was achieved with a small lasing wavelength fluctuation up to 1.2 nm at RT-CW condition under optical pumping. From this value, membrane thickness fluctuation was estimated to be 0.4 nm. Threshold pump power of 3.4 mW and SMSR of 45 dB were achieved in a typical device.

Strongly Index-Coupled Membrane BH-DFB Lasers With Surface Corrugation Grating

We realized strongly index-coupled membrane buried-heterostructure (BH) distributed-feedback (DFB) lasers fabricated by electron-beam lithography, CH4/H2 reactive-ion etching, and regrowth by organometallic vapor-phase epitaxy, using surface corrugation DFB. First, we fabricated narrow stripe membrane BH-DFB lasers with surface corrugation for stable single-mode operation. Under optically pumped room-temperature continuous-wave (RT-CW) operation, a wide stopband width of 68 nm was observed in spite of the narrow stripe width of 0.6 mum. The corresponding index-coupling coefficient of 2950 cm-1 is over two times larger than that of a flat-surface (conventional) membrane BH-DFB laser with a stripe width of 2.0 mum. In addition, we fabricated a short-cavity membrane DFB laser with a surface corrugation structure. A threshold optical pump power of as low as 0.34 mW was realized for a 2.0-mum-wide and 80-mum-long device under RT-CW conditions.

Low-threshold and high-efficiency operation of distributed reflector lasers with width-modulated wirelike active regions

1.55-/spl mu/m-wavelength distributed reflector (DR) lasers with low threshold and high efficiency were realized which consisted of a distributed feedback (DFB) grating and high-reflection distributed Bragg reflector (DBR) sections integrated by utilizing the lateral quantum confinement effect in a quantum-wire structure. In order to realize a high-performance DR laser, the high-reflection DBR structure was investigated theoretically and experimentally and could be fabricated with a reflectivity of over 90%, taking into consideration the absorption in the active layers. The highest differential quantum efficiency of 36% from the front facet was obtained for the 4.4-/spl mu/m stripe width and 300-/spl mu/m DFB section length under room temperature (RT) and continuous-wave (CW) conditions. Moreover, the lowest threshold current of 1.5 mA was obtained for the 3.4-/spl mu/m stripe width and 150-/spl mu/m DFB length.

Low threshold current density operation of GaInAsP-InP laser with multiple reflector microcavities

We propose and demonstrate a new type of semiconductor laser having multiple reflector microcavities for the purpose of low threshold current operation. Very uniform multiple reflector microcavity structure was fabricated by electron beam (EB) lithography and selective wet chemical etching. Due to multiple reflection effect, threshold current density as low as 310 A/cm/sup 2/ (threshold current of 30 mA) was obtained at room temperature with the total cavity length of 64 /spl mu/m and the cavity width of 200 /spl mu/m.<<ETX>>

GaInAsP/InP Partially Strain-Compensated Multiple-Quantum-Wire Lasers Fabricated by Dry Etching and Regrowth Processes

This paper reports the structural properties and lasing characteristics of GaInAsP/InP multiple-quantum-wire lasers fabricated by electron beam lithography, CH4/H2-reactive ion etching and organometallic vapor-phase-epitaxial regrowth. Good size distributions of multiple-quantum-wire structures (wire widths of 18 nm and 27 nm in a period of 80 nm) have been obtained with standard deviations less than ±2 nm. We have confirmed that low-damage etched/regrown interfaces of quantum-wire structures can be realized by using a partially strain-compensated quantum-well structure. Threshold current densities of 5-quantum-well wirelike lasers (wire widths of 43 nm and 70 nm) were found to be lower than that of the quantum-film laser, fabricated from the same initial wafer, due to a volume effect at temperatures up to 85°C. Finally, room temperature (RT)-continuous wave (CW) operation of multiple-quantum-wire lasers (wire width of 23 nm in a period of 80 nm, 5-stacked quantum-wires) was achieved, and the good reliability of this quantum-wire laser was demonstrated for the first time by means of lifetime measurement under the RT-CW condition.

GaInAsP/InP Multiple-Layered Quantum-Wire Lasers Fabricated by CH4/H2 Reactive-Ion Etching

GaInAsP/InP multiple-layered quantum-wire lasers with the wire width of 21 nm in the period of 100 nm were realized by CH4/H2 reactive-ion etching followed by slight wet chemical etching and embedding growth by organometallic vapor phase epitaxy. A threshold current density as low as 1.45 kA/cm2 was obtained with the cavity length of 980 µm. To our knowledge, this is the lowest value reported for 1.55 µm GaInAsP/InP quantum-wire lasers fabricated by the etching and regrowth method. Because of the temperature dependence of the lasing wavelength, a relatively large blue shift of 47 meV in the quantum-wire laser was observed, which can be attributed to not only a lateral quantum confinement effect but also a three-dimensional compressive strain effect. Finally, we improved the initial wafer structure in order to suppress over-etching of the active region, and obtained lasers consisting of a five-layered wirelike active region with good size uniformity (wire width of 42 nm, period of 120 nm). A threshold current density as low as 540 A/cm2 was obtained with the cavity length of 1.38 mm.

1.5-µm-Wavelength Distributed Feedback Lasers with Deeply Etched First-Order Vertical Grating

1.5-µm-wavelength distributed feedback lasers with a deeply etched first order vertical grating were realized for the first time. It was shown that we can obtain an effective coupling by reducing the stripe width. The sample with the cavity length of 430 µm, 1.8 µm stripe width and 0.2 µm grating depth on each lateral side exhibited a 12.5 mA threshold current, 37% total differential quantum efficiency and 35 dB submode suppression ratio at a bias current of two times the threshold.

Room-temperature operation of GaInAs/GaInAsP/InP SCH lasers with quantum-wire size active region

Improvements in the fabrication of GaInAs(P)/InP devices consisting of an ultrafine structure by using two-step organometallic vapor phase epitaxy (OMVPE) growth, electron beam exposure direct writing, and wet chemical etching are reported. This improved process achieved, for the first time, a room-temperature continuous-wave (CW) operation of GaInAs/InP quantum-wire lasers consisting of 5-nm-thick and 10-30-nm-wide vertically stacked triple quantum-wire active region within the period of 70 nm. A large blue shift of approximately 40 nm was observed in both the lasing and the electroluminescence spectra of Ga/sub 0.3/In/sub 0.7/As/InP compressively strained multi-quantum-well (MQW) wire lasers consisting of a 3-nm-thick and 30-60-nm-wide five-wire active region, which suggests a reduced effective mass of holes along the in-plane direction. >

Multiple-wavelength membrane BH-DFB laser arrays

We realized multiple-wavelength laser arrays based on a membrane buried-heterostructure distributed-feedback (BH-DFB) structure fabricated by electron-beam lithography (EBL), CH/sub 4//H/sub 2/ reactive-ion etching, and regrowth by organometallic vapor-phase epitaxy (OMVPE), and investigated their wavelength controllability using two different approaches, i.e., a modulation of the DFB grating period and that of the stripe width. Under optically pumped room-temperature continuous-wave (RT-CW) operation, a wavelength fluctuation for a fixed DFB grating period was found to be less than /spl plusmn/1.2 nm for all 75 samples prepared on the same wafer. A total wavelength span of 64 nm and an average channel spacing of 3.4 nm were obtained in the DFB period modulation range of 311.25 to 335.00 nm with 1.25-nm steps. An average channel spacing of 4.1 nm was also obtained in the stripe modulation range of 1.0-2.8 /spl mu/m with 0.2-/spl mu/m steps.