For visible-light-emitting laser diodes, InGaAsP double heterostructures have been grown on GaAs substrates using liquid-phase epitaxy. As the growth temperature is as high as about 780 °C, a large amount of phosphorus evaporates from the solutions for the cladding layers during the growth process. The phosphorus vapor disturbs the solution composition for the active layer, so that very thin and uniform active layers cannot be obtained. By using In-P-Sn solution and supplying the phosphorus partial pressure around the graphite boat, the influence of phosphorus vapor ambient for InGaAsP (λPL=805 nm) growth is confirmed. When the phosphorus partial pressure increases, the surface of epitaxial layer becomes rough and the substrate is partly etched back. From x-ray diffraction and photoluminescence spectral measurements, the composition of the grown layer is also found to be changed. As a result of increasing the flow rate of H2 gas in order to protect the solution for the active layer from phosphorus contamination, the double heterostructure wafers with the high-quality active layer can be obtained reproducibly. Thus, pulsed lasing operation at room temperature has been achieved. The lasing wavelength is 816 nm and the threshold current density is ∼4.6 kA/cm2.

New double-heterostructure indium-tin oxide/InGaAsP/AlGaAs surface light-emitting diodes have been fabricated by liquid-phase epitaxy and rf sputtering methods. In this structure, indium-tin oxide acts as both an n-type cladding layer and a transparent conductor. Peak wavelength and full width at half maximum of the surface emitting spectrum were 653 and 17 nm, respectively. An output power of 1 mW was achieved at a current level of 66 mA, corresponding to a current density of 22 A/cm2 under pulsed operation for the diode with a 400 μm×450 μm emitting area. The optical emission was distributed over the entire emitting area.

Liquid-phase-epitaxial (LPE) growth of AlGaAs layers has been used in fabricating InGaAsP buried heterostructure visible lasers on GaAs substrate. InGaAsP/InGaAsP double heterostructure wafers were grown on the p-type GaAs substrates by means of the melt-back method prior to the LPE growth for eliminating phosphorus contamination. An SiO2 film mask was deposited on the epitaxial wafer surface by the rf sputtering, and photoetched with stripes of 7–10 μm width in the 〈110〉 direction. After etching to the first p-InGaAsP cladding layer with a 3% Br-methanol solution, the second LPE growth of n-AlGaAs and p-GaAs layers was carried out. The InGaAsP active region is entirely surrounded by the InGaAsP cladding layers and the AlGaAs burying layer, therefore, it becomes possible to provide both lateral and vertical carrier and optical confinements. I-L characteristics were measured at room temperature under pulsed operation, but the lasing action was not obtained. The peak wavelength of the electroluminescence was 785 nm. The transverse mode behavior was analyzed by means of the effective refractive index approximation. And it seemed that this buried heterostructure is suitable for the transverse mode control of InGaAsP visible laser diodes.

A simple method for the fabrication of Fabry–Perot mirrors of InGaAsP/GaAs lasers is presented. The vertical and smooth wall etching is done for active layers only (not for both active and cladding layers), by an H2SO4:H2O2:H2O=3:1:1 etchant for 2–5 s. Since the active layers are much thinner than the cladding layers, the etching becomes much easier. The threshold current density of the etched mirror laser is ∼4.4 kA/cm2, about 1.1 times that of the cleaved laser, and the mirror reflectivity is evaluated as 29.4% (cleaved 31.4%).

The internal loss α and gain factor β of InGaAsP/GaAs double-heterostructure lasers were examined by immersing laser chips into various liquids and changing the reflectivities of a Fabry-Perot mirror. Only a small scatter was found; we evaluated α and β as 20.6 cm-1 and 0.0129 cm·A-1, respectively. The value of α was compared with the loss of AlGaAs/GaAs lasers.