Laser Wafers Research Articles

Improvement of GaAs-GaAlAs double-heterostructure laser wafer by Ga1−xAlxAs buffer layer

The optically induced degradation in GaAs-GaAlAs double-heterostructure (DH) laser wafers is examined at elevated temperatures. The degradation of the photoluminescence properties by optical pumping is considered to originate at the interface between an n-GaAlAs clad layer and a p-GaAs active layer, as it is greatly reduced by the insertion of a thin Ga1−xAlxAs buffer layer (x∼0.05, ∼0.05 μm thick) between these two layers. The degradation rate during optical pumping is correlated to laser life. The lasers fabricated from the DH wafers with the Ga1−xAlxAs buffer layer are still operating after 2000 h at 70 °C, whereas lasers without the buffer layer are inoperative after a few hundred hours.

Very low current threshold GaAs-AlxGa1−xAs double-heterostructure lasers grown by molecular beam epitaxy

GaAs-AlxGa1−xAs (x=0.3) double-heterostructure (DH) lasers having very low current threshold densities have been prepared by molecular beam epitaxy (MBE). For DH lasers having Al-mole-fraction differences between the active layers and AlxGa1−xAs confinement layers Δx∼0.3, the best of the MBE-grown DH laser wafers have averaged current threshold densities similar to those obtained from the best of similar-geometry DH lasers prepared by liquid-phase epitaxy (LPE) and by metalorganic chemical vapor deposition (MO-CVD). With Δx=0.3, the lowest averaged current threshold density achieved is 800 A/cm2 (without reflective coating) for a wafer with an active layer thickness of 0.15 μm.

High-resolution composition profiling of GaAs-AlxGa1−xAs double-hetero-laser structures with photoluminescence

Measurements of composition of multilayer semiconductor laser wafers were performed with the aid of photoluminescence spectra. Reliable depth profiling of composition is difficult in as-grown wafers, even at low temperature, because the excess-carrier diffusion length is comparable to the layer thicknesses. With adequate reduction of the diffusion length, which in our case was done with ion implantation, the origin of photoluminescence could be restricted to a narrow region close to the excited surface. Samples were prepared for profiling by an angle-etching technique, leaving a controlled angle as small as 0.01° across the wafer, which greatly simplifies profiling measurements. Results from composition profiling of a conventional five-layer GaAs-AlxGa1−xAs DH-laser wafer with a depth resolution better than 0.1 μm are presented.

Multiple liquid phase epitaxy of In1−xGaxP1−zAsz double-heterojunction lasers: The problem of lattice matching

Multiple liquid phase epitaxy of In1−xGaxP1−z Asz-InP double heterojunctions, from a single set of In-rich melts, is demonstrated, and is shown to be a useful technique for the study of the problem of lattice matching at heterojunction interfaces and for growing large numbers of low-threshold (’’defect-free’’) DH laser wafers (λ∼1 μm).