Optical transverse-mode properties of the GaN-based semiconductor laser-diode is characterized by effective refractive index method. In order to stabilize a transverse-mode in the conventional ridge-waveguide structure, very precise control of ridge-height is found to be necessary. On the contrary, a novel 2-step grown structure with 2-dimensional index guiding has wide feasibility for device parameter, excellent stability of large confinement factor in transverse-mode, and small aspect ratio of beam divergence, under the condition that AlN molar fraction of 0.08 in AlGaN current blocking layer and stripe width of 1.5 µm are used.

The correlation between ohmic contact resistivity (ρc) and transconductance (gm) in AlGaN/GaN high-electron-mobility transistors (HEMTs) was investigated. To characterize ρc precisely, we fabricated a circular transmission line model (c-TLM) pattern adjoined to a field-effect transistor (FET) pattern on an HEMT. By measuring ohmic contact resistance and sheet resistance using the adjoined c-TLM, intrinsic transconductance (gm0), which is not influenced by the source resistance, can be estimated. The gm0 thus obtained is between 179 and 206 mS/mm. Then, it became possible to calculate the correlation between gm and (ρc. We found that ρc should be below 10-5 Ωcm2 for the improvement of gm in AlGaN/GaN HEMT when Rsh 400 Ω/.