Nondestructive Evaluation of Detuned Wavelength for As-Grown VCSEL Epi-Wafer

We propose a nondestructive method to estimate the peak wavelength of the active quantum well (QW) region of an as-grown vertical-cavity surface-emitting laser (VCSEL) epi-wafer based on room temperature electroluminescence (EL) measurements. Contacts for the electrical excitation are established using flexible conductive materials on the epilayers without the fabrication of metal electrodes. The angle dependence of the EL properties is investigated to analyze the detuned wavelength of the active QW region for the VCSEL structure. The wavelength offset caused by detuning obtained from the as-grown epi-wafer correlates with the laser threshold properties of the VCSEL chips fabricated from the epi-wafer. The results show the possibility of a nondestructive evaluation method without metal electrodes for as-grown VCSEL epi-wafers, particularly the active QW region, which has been challenging to optically analyze from completed VCSEL epi-structures.