Results 1994

A new type of multiple-reflector micro-cavity laser was proposed and analyzed.
A linewidth property of complex coupled DFB laser was analyzed and fabricated.
A GaInAsP/InP semiconductor collimating GRIN lens was proposed and fabricated for optical coupling improvement of SLA and LD to single mode fiber.

Results obtained in this research are as follows.

(1) A new type of multiple-reflector micro-cavity laser having a 30% refractive index difference was proposed, and it was found that it is possible to operate on sub-mA current.

(2) The cavity length dependence of the linewidth property of complex coupled (CC) DFB lasers was analyzed.

(3) A 1.55 micro meter wavelength CC-DFB laser having an anti-phase structure by introducing InP depression layer was fabricated. We showed the ratio of the index-coupling coefficient to the gain-coupling coefficient can be controlled by introducing this InP depression layer.

(4) Saturation characteristics of TTW-SLA using the tensile strained quantum well active layer was demonstrated.

(5) A semiconductor collimating GRIN lens for vertical output beam divergence improvement of SLA and LD was fabricated, and integration with TTW-SLA was demonstrated.

Ga1-xInxAs/GaInAsP/InP strained-quantum-film, -wire, and -box lasers have been studied both theoretically and experimentally. By introducing tensile-strained quantum-wire (QW) structure into the active layer, room temperature CW operation of GRIN-SCH single-QW lasers with fairly low threshold current was achieved. GaInAs/GaInAsP (strained-) quantum-box (QB) structures were fabricated and obvious 0-dimensional QB size effects were observed. Temperature dependences of lasing properties were measured and compared with those of quantum-film lasers. Carrier injection process in SCH quantum-film and wire lasers was investigated.

The results obtained in this research are as follows.

(1) Temperature dependence of lasing properties of quasi-quantum-wire lasers were measured and compared with those of quantum-film lasers.

(2) By combining electron beam lithography and ECR dry etching, 20-30nm wide GaInAs/GaInAsP multi-quantum-wire and -box structures with the aspect ratio greater than 6 were realized. Moreover, low damage feature of this fabrication process was confirmed by PL observation.

(3) An emission energy level shift due to obvious 0-dimensional quantum- box effect was observed at 4K with GaInAs/GaInAsP single-layer (strained-) embedded quantum-box structures.

(4) Lasing action of Ga0.67In0.33As/GaInAsP/InP tensile-strained quantum-box laser was demonstrated for the first time. The fabricated QB size is 30nm diameter and 12nm thick with a period of 70nm. The threshold current density was 7.6KA/cm2 at 77K with pulse current injection.

(5) Carrier capture time of SCH-QW-lasers was measured by the spontaneous emission spectra above threshold. Difference between unstrained, tensile-strained, and compressive-strained lasers was obtained.

Study of nanometer structure fabrication technique is important for the realization of quantum effect devices such as quantum-wire or -box devices and ballistic electron devices based on wave characteristics of electrons.

Results obtained through this year are as follows.

(1) Ultrafine fabrication technique for hot electron interference diffraction devices was proposed using electron beam direct writing lithography and OMVPE. An alignment of 70nm pitch buried GaInAs /InP heterostructure and 70nm pitch electrodes was demonstrated for the first time.

(2) A cross-sectional multiple quantum well structure (GaInAs:3nm/ GaInAsP:8nm) was observed clearly by a scanning tunneling microscope (STM) in air. (NH₄)₂S_x solution was used for passivating the sample surface. In addition, the relation between the pulse voltage/time and the size of modified area was also investigated.

(3) Anodization process of InP: Anodization process of InP has been investigated with aiming at a novel fabrication technology of quality quantum-wire and quantum-box structures. As the result, a high density (space filling factor of 50%), uniformly shaped (triangle) and sized (40nm) vertical pillar structure was obtained on (111)A oriented InP substrate with a SiO₂ mask by adopting an EBX direct patterning followed by the anodization with HCl acid. Very small physical damage by anodization process was established from observing strong PL intensity from 40nm size-ordered triangle pillers.