Nhng tin b trong Quang hc, Quang ph và ng dng VI ISSN 1859 - 4271

Những tiến bộ <strong>trong</strong> <strong>Quang</strong> học, <strong>Quang</strong> <strong>ph</strong>ổ và Ứng dụng VI ISSN 1859 - 4271STRAIN MEASUREMENT IN HIGH-POWER DIODE LASERS BYPHOTOCURRENT SPECTROSCOPYTran Quoc Tien 1 and Jens W. Tomm 21 Institute of Materials Science, VAST, 18 Hoang Quoc Viet, Cau giay, Hanoi, Vietnam2 Max-Born-Institut, Max-Born-Str. 2 A, 12489 Berlin, GermanyEmail: tientq@ims.vast.ac.vnAbstract. We report an application of Photocurrent Spectroscopy to investigate of the mechanicalstrain in semiconductor structures. Under the mechanical strain, the electronic band structure ofquantum-well semiconductor is modified and leads to a change of the absorption peaks in <strong>ph</strong>otocurrentspectra. Therefore the strain inside the quantum-well semiconductor structures can be quantified byanalyzing the shift of these peaks with Fourier-Transform Photocurrent Spectroscopic technique andprovide a nondestructive and non-time-consuming method for strain investigation of high-power diodelasers that is related to reliability of the devices. Our studies on strain of these devices can be extendedfor other semiconductor optoelectronic devices.Keywords: high-power, diode lasers, <strong>ph</strong>otocurrent spectroscopy, mechanical strain.I. INTRODUCTIONExternal strains are one major source of degradation processes occurring in high-power diodelaser (HPDL) arrays. Therefore, the understanding of strain behaviours of these devices (nature,mechanisms and interactions with other parameters) is urgently needed. After the packagingprocess, the HPDLs experience a total strain including the following strain contributions [1-4]:the misfit strain contribution created during the growing process of the laser structures becausethe lattice constants of epitaxial layers are mostly different compared to the substrates; thedifferent thermal expansion coefficients of epitaxial layers and substrates cause strain, when thestructure cools down from growing to ambient temperature; the processing-induced straincontribution that is consequence of post-growing processes before packaging, e.g., duringmetallization, polishing; the packaging-induced strain caused by the packaging process of theHPDL chips, which are cleaved from wafer, onto the heatsink; the strain due to the creation ofdefects that might be generated in HPDL structures, e.g. during operation. While the first straincontribution belongs to the intrinsic strains, the others are considered external strains. Theabsorption spectra reflect the modification of electronic band structure in the semiconductordevice that caused by strain [3,4]. Therefore, to investigate these sources of strain, we consideran absorption related method, namely PCS. This method is combined to Fourier transformtechnique provide a very efficient non-destructive tool for reliability investigation of HPDL oroptoelectronic devices in general.In this paper, first, we introduce the method to investigate strain in quantum well (QW)optoelectronic semiconductor structures including theoretical background and experimentaltechnique. After that, some pratical results measured on HPDLs will be demonstrated. Thediscussion on strain behaviour of these devices will also be done as well.123