Kyohei Doi

Room-temperature continuous-wave operation of GaInAsP/InP lateral-current-injection membrane laser bonded on Si substrate

We successfully demonstrated room-temperature continuous-wave (RT-CW) operation of a lateral-current-injection (LCI) GaInAsP/InP membrane Fabry–Perot laser by benzocyclobutene (BCB) adhesive bonding on a Si substrate for the first time. Our results include, for example, a threshold current of 2.5 mA and an external differential quantum efficiency of 22% per facet were obtained for a stripe width of 0.7 µm and a cavity length of 350 µm. From measurements of the differential quantum efficiency as a function of the cavity length, an internal quantum efficiency of 75% and a waveguide loss of 42 cm−1 were obtained.

Thermal Analysis of Lateral-Current-Injection Membrane Distributed Feedback Laser

We theoretically investigated the self-heating effect caused by current injection into a membrane distributed feedback laser designed to operate at ultralow-power consumption. By simulating its temperature distribution, the thermal resistance of the laser was estimated to be 6100 K/W. In addition, changes in lasing characteristics owing to the self-heating effect were calculated. An output power of 0.18 mW - which is adequate for an on-chip light source - can be obtained at a driving power of 1 mW. We proved that, owing to its ultralow-threshold operation, the self-heating effect has little effect on the lasing characteristics of the membrane laser.

Design of Lateral-Current-Injection-Type Membrane Distributed-Feedback Lasers for On-Chip Optical Interconnections

For application to on-chip optical interconnections, lateral-current-injection (LCI) membrane distributed-feedback (DFB) lasers, which are expected to be potential components for such an application, were investigated from the aspects of low threshold current operation and high-speed direct modulation capability. First, the stripe width dependence of the carrier injection delay time was evaluated from small-signal response measurements of LCI Fabry-Perot lasers prepared on a semi-insulating InP substrate, and it was found that a narrower stripe width was advantageous for shorter carrier injection delay time as well as higher internal quantum efficiency. Second, semiconductor core layer thickness dependences of the lasing properties of LCI-membrane-DFB lasers, such as the threshold current, output power, relaxation oscillation frequency, and a 3-dB bandwidth, were investigated theoretically. A strong optical confinement effect in the semiconductor membrane structure enabled the design of an LCI-membrane-DFB laser with a low threshold current of 0.16 mA, an output power of more than 0.16 mW, and a high relaxation oscillation frequency of 8.9 GHz at a bias current of only 1 mA. From these values, the LCI-membrane-DFB laser can be a good candidate for a low-pulse-energy (<;100 fJ/bit) light source, for high-speed (>10 Gb/s) transmission, and for on-chip optical interconnections.

Low-threshold operation of LCI-membrane-DFB lasers with Be-doped GaInAs contact layer

One of the promising candidates to solve a problem of a performance limitation of LSI is replacing electrical global wirings by on chip optical interconnections. We proposed and realized lateral-current-injection (LCI) type membrane DFB lasers for this purpose. In this paper, we report a new type LCI membrane DFB laser by introducing Be-doped GaInAs contact layer to the initial wafer structure so as to make simple fabrication of p-contact. As the result, a threshold current of as low as 3.8 mA, which was much lower than the previously reported value of 11 mA, was obtained for the stripe width of 1.5 μm and the cavity length of 250 μm.

Energy Cost Analysis of Membrane Distributed-Reflector Lasers for On-Chip Optical Interconnects

The power consumption of lateral-current-injection semiconductor membrane distributed-reflector lasers with a λ/4 shift region has been theoretically evaluated, in terms of their ultralow-power-consumption and high-speed modulation operations. This paper contains an investigation into the optimal structure of the membrane laser in terms of its energy cost, for use in on-chip optical interconnections. The total power consumption was evaluated, taking Joule heating into account by assuming the device resistance. It was found that the large Joule heating effect present in shorter cavities limits a reduction of their power consumption. As a result, an energy cost of 63 fJ/bit can be obtained for 10 Gb/s data transmission, while maintaining the necessary power output required for a cavity length of 12 μm. We have provided a guide for designing microcavity lasers in terms of their Joule heating power.

Room-temperature continuous-wave operation of lateral current injection membrane laser

Toward realization of an ultralow-power-consumption semiconductor light source for optical interconnection, we have been investigating the lateral current injection (LCI) membrane distributed feedback (DFB) laser. This time, we realized membrane Fabry-Perot (FP) laser with 220 nm core thickness and demonstrated room-temperature continuous-wave (CW) operation with a threshold current of 3.5 mA for the cavity length of 700 μm and the stripe width of 1.0 μm, which is almost the same as the theoretical value.

Improved quantum efficiency of GaInAsP/InP top air-clad lateral current injection lasers

An internal quantum efficiency (ηi) of GaInAsP/InP top air-clad lateral current injection (LCI) lasers was considerably improved by covering the top surface with 50-nm thick InP cap layer. As the result, threshold current of 6.7 mA and the differential quantum efficiency of 56% were attained for five-quantum-wells (QWs) LCI laser with the cavity length of 500 μm and the stripe width of 1.5 μm.

Butt-joint built-in (BJB) structure for membrane photonic integration

On-chip optical interconnections have potential for replace global copper wires on LSI chips. I n this work, as an integration method, an OMVPE butt-joint regrowth of 175-nm thick GaInAsP/InP was conducted toward an integration of active and passive components. In the numerical calculation, a coupling efficiency and residual reflection of designed butt-joint coupling were estimated to be 98% and -40 dB, respectively. In the experimental method, we investigated the dependence of butt-joint interface morphology and regrown surface flatness on the side etch depth and the mesa angle. As a result, a flat regrown surface without degradation in crystalline quality was obtained.

Low-threshold-current operation of lateral current injection membrane distributed-feedback laser bonded on Si

Toward realization of an ultralow-power-consumption semiconductor light source for on-chip optical interconnection, we have been investigating the lateral current injection (LCI) membrane distributed feedback (DFB) laser. This time, we realized membrane DFB laser with 158 nm core thickness and demonstrated room-temperature continuous-wave (CW) operation with a threshold current of 390 μA for the cavity length of 360 μm and the stripe width of 0.2 μm, which is lowest value ever reported in a DFB lasers on a Si substrate.

Low-power and high-speed operation capabilities of semiconductor membrane lasers — Energy cost limited by Joule heat

The power consumption of a lateral current injection (LCI) type membrane distributed reflector (DR) laser under a high-speed direct modulation was theoretically investigated. As the results, we found that there is an optimal cavity length, which can be determined by the series resistance, to minimize the power consumption. For an example., an energy cost of 37 fJ/bit can be obtained at a modulation speed of 10 Gb/s for the cavity length of 17 μm when the grating coupling coefficient of 1800 cm-1 and the resistivity of p-InP cladding layer of 0.035 Ω·cm are used.