Circular buried heterostructure (CBH) GaAlAs/GaAs surface emitting lasers

For the purpose of introducing a current confining structure to the GaAlAs/GaAs surface emitting (SE) laser, a circular buried heterostructure (CBH) was introduced. The selective meltback/regrowth was employed as a novel burying method of the CBH-SE laser. First, a difference of the meltback-speeds for various AI contents of GaAlAs layers was measured by observing the depth of dissolved groove. For example, the meltback speed for GaAs was 1.6 μm/s and was almost 3 times as fast as that for Ga
0.7
Al
0.3
As. Next, an edge emitting BH stripe laser was fabricated by the selective meltback/regrowth method. The nominal threshold current density of this device was almost the same as that of the DH broad contact laser (≅ 8 kA/cm
²
/μm). The typical threshold current of CBH-SE lasers was reduced to ∼ 80 mA with a minimum of 68 mA when the active region was
\sim 15 \mu
m in diameter under pulsed conditions at room temperature. But one extremely low threshold device with an active region of
\sim 6 \mu
m in diameter was realized. The threshold was 6 mA (300 K, 1 μs pulse) and 4.5 mA (77 K, CW). This means that the diffraction loss is not noticeable when the diameter is
> 6 \mu
m. This is also the first demonstration of a microcavity GaAlAs/GaAs surface emitting laser with a cavity of 7 μm long and 6 μm in diameter.