Research : Quantum-Wire Laser

Realization of high-performance photonic devices with ultra fine structures

Quantum-film (Q-Film) lasers have been adopted for various applications. By the introduction of low-dimensional quantum-well structures, such as quantum-wire (Q-Wire) and quantum-box (Q-Box or Q-Dot) structures, carriers are confined to them stronger than to Q-Film due to density of states distributions of Q-Wire and Q-Box structures are sharper compared with those of the Q-Film structure as shown in Fig. 1. Higher optical gain and narrower gain spectrum properties of Q-Wire and Q-Box structures are obtained due to a sharper density of states feature as shown in Fig. 2. Consequently, it has been expected that the consumption electric power and the efficiency of Q-Wire and Q-Box lasers are superior to those of Q-Film lasers. The modulation speed and the linewidth might also be improved.

Although various methods have been studied in order to fabricate Q-Wire and Q-Box lasers, we have been investigating a fabrication method, which combines electron beam (EB) lithography, dry etching and organometallic vapor-phase-epitaxial (OMVPE) regrowth because of a better position controllability and wider applications than other methods. Furthermore, this fabrication method is very effective in the production of distributed feedback (DFB) lasers.

By using this fabrication method, the low-damage etched/regrown interface of GaInAsP/InP fine structures was realized, and the reliable room temperature (RT)-continuous wave (CW) operation of Q-Wire lasers was attained for the first time.

(Ⅰ) Strain-compensated quantum-wire lasers

We realized a RT-CW operation of GaInAsP/InP quantum-wire lasers (wire width of 23 nm in a period of 80 nm, 5-stacked quantum-wires) fabricated by EB lithography, CH4/H2-reactive ion etching and 2-step OMVPE growth processes for the first time. From RT-CW lifetime measurement, no noticeable performance degradation was observed even after more than 12,000 hours. Good size distributions of multiple-quantum-wire structures have been obtained with standard deviations less than ±2 nm.

GaInAsP/InP quantum-wire lasers with narrow wire structures (wire width of 14 nm in a period of 80 nm, 5-stacked quantum-wires) were realized. Lateral quantum confinement effect in this quantum-wire laser could be observed via sharper shape of the EL spectrum than that of quantum-film lasers in the higher transition energy region.

In future, we aim to realize the narrow spectral width with good size uniformity of quantum-wires and the low threshold current operation of Q-Wire lasers by applications of distributed Bragg reflector (DBR) structure and DFB cavity.

(Ⅱ) Photonic devices with arbitrary shaped low-dimensional structures

In quantum-wire structures with a strong lateral quantum confinement effect, the optical electric field of the parallel direction to the quantum-wire is stronger than that of the perpendicular direction to the quantum-wire. Energy levels for the radiation and the absorption having the polarization anisotropy can also be changed by the variation of the wire width. Accordingly, we will investigate arbitrary shaped low-dimensional quantum-well structures with good position controllability for the application to various photonic devices.

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Nishiyama Laboratory
School of Engineering Dept. of Electrical and Electronic Engineering, Institute of Science Tokyo

7F, S9-1, 2-12-1 O-okayama, Meguro-ku Tokyo 152-8552, Japan +81-3-5734-2555 ee.e titechnishiyama

Nishiyama lab. Student's room : South Bldg. 9 #701, #706, #707 | Measurement room : South Bldg. 9 #604, #502, #201 |
Clean room : South Bldg. 9 #202, B1F Exposure house | Research Laboratory of Ultra-High Speed Electronics