Thermoreflectance Measurements of the Temperature Distributions in Laser Diodes with Non Injected Facet
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0916-DD06-01
Thermoreflectance Measurements of the Temperature Distributions in Laser Diodes with Non Injected Facet Tomasz Ochalski1, Dorota Pierscinska1, Kamil Pierscinski1, Andrzej Malag2, Agata Jasik2, Anna Kozlowska2, and Maciej Bugajski1 1 Institute of Electron Technology, Al. Lotników 32/46, Warsaw, 02-668, Poland 2 Institute of Electronic Materials Technology, 133 Wolczynska St., Warsaw, 01-919, Poland 1. INTRODUCTION In a standard edge-emitting laser, the facet heating mechanism can be described in the following way1. The non-radiative surface recombination at the semiconductor-air interface locally rises the temperature. Higher temperature causes the band gap energy shrinkage. This, in turn, causes the increase of the temperature due to higher absorption of the light. Finally, the positive feedback mechanism leads to catastrophic optical damage (COD)2 of the laser mirror and, in consequence, to the destruction of the device. This undesired process can be to certain extend controlled by the reduction of carrier concentration in the vicinity of the facet and hence suppressing heating due to the non-radiative recombination. Following this reasoning we examine the laser diode structure with Non Injected Facet (NIF), i.e., with the stripe contact retracted from the edge of the structure. These NIF lasers should have reduced surface recombination current due to the non injected area close to the facet. The proposed approach is similar in the idea to introducing current blocking layer close to the facet3. A laser diodes with Non Injected Facet (NIF) were analysed with respect to the mirror temperature distributions. The facet heating in high-power devices has been studied by means of non-invasive optical technique: thermoreflectance 4,5,6. 2. EXPERIMENT
In this work we present the analysis of thermal properties of two kinds of GaAsP/AlGaAs laser diodes: NIF and standard laser diode. We have used microthermoreflectance (µTR) spectroscopy to determine facet temperature. Thermoreflectance is a modulation technique relying on periodic facet temperature modulation induced by pulsed current supply of the laser. The periodic temperature change of the laser induces variation of the refractive index and consequently modulates probe beam reflectivity7. The principle of the thermoreflectance modulation technique is based on the dependence of the sample’s reflectance on the temperature. A variation in the sample reflectance (∆R) is related to the temperature variation (∆T) through the following relation: −1
∂R ⎞ ∆R ∆R (1) ∆T ≡κ ⎟ ∂T ⎠ R R The thermoreflectance calibration coefficient κ depends on the material8, on the specific details of the experimental set-up (numerical aperture of the microscope objective)9, and most importantly, on the wavelength of probe light10. Due to this fact the coefficient κ should not be taken ⎛1 =⎜ ⎝R
from the literature, but should be determined experimentally. The technique has a spatial resolution below 1µm and temperature accuracy better than 1 degree. Scheme of our thermoreflectance se
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