Reduction of RIE Induced Damage of GaInAsP/InP DQW Lasers Fabricated by 2-step Growth

摘要

In order to realize low damage fine structuring processes for the low-dimensional quantum structures, we investigated a process for reducing the degradations of optical properties, which was induced during a reactive-ion-etching (RIE) process with CH_4/H_2gas mixture in the quantum-well (QW) structures. Quantitative studies of optical degradation were carried out by photoluminescence (PL) and electroluminescence (EL) measurements. We introduced a thicker upper optical confinement layer (OCL) to protect the QWs from the RIE-plasma. In practical, for the PL measurement, two-types of strain-compensated single-quantum-well (SC-SQW) structures were prepared for 40-nm-thick- and 80-nm-thick- upper OCL wafers and covered by 20-nm-thick SiO_2. After the samples were exposed to CH_4/H_2-RIE for 5-minutes, a relatively stronger suppression of integral PL intensity as well as a spectral broadening was observed in the sample with 40-nm-thick OCL, while those did not change in the sample with 80-nm-thick OCL. For the EL measurements, using two types of SC-DQW structures, samples were exposed to CH_4/H_2-RIE plasma for 5-minute and then re-grown for other layers to form high-mesa stripe laser structures (W_s=1.5μm). As a result, the spontaneous emission efficiency of the lasers with 80-nm-thick OCL was almost 2 times higher than that of the lasers with 40-nm-thick OCL. In addition, a lower threshold current as well as a higher differential quantum efficiency was obtained for the lasers with 80-nm-thick OCL , while that in lasers with 40-nm-thick OCL indicated poor efficiency and a slightly higher threshold.