Analysis of the Front Facet Temperature in Laser Diode With Non Absorbing Mirror
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0891-EE03-26.1
Analysis of the Front Facet Temperature in Laser Diode With Non Absorbing Mirror Tomasz Jan Ochalski1, Dorota Pierscinska1, Andrzej Malag2 Institute of Electron Technology, Warsaw, Poland 2 Institute of Electronic Materials Technology, Warsaw, Poland 1
ABSTRACT Non-absorbing mirror (NAM) lasers, also known as window lasers, were developed to increase catastrophic optical damage level of the devices1. In this work we present the analysis of the laser diodes (LD) front facet temperature distribution. Micro-thermoreflectance technique is used to perform a detailed temperature maps of the operating LDs. Such a technique gives us temperature maps with a high spatial resolution equal 0.6µm. We demonstrate micro thermoreflectance as a perfect tool to determine real temperature distribution of the operating laser diode front facet. INTRODUCTION The performance of diode lasers is strictly related to the temperature distribution in the laser structures and thus depends on the laser design, materials used for its construction and operating conditions. In this work we study temperature distributions at the mirrors in high power broad area laser diodes (LD). It should be noted that the temperature at the facet plays a critical role in device reliability and performance. We will present 2D maps of relative temperature T distribution for p-side down mounted GaAsP/AlGaAs quantum well lasers with non absorbing mirrors (NAM). The experimental results were obtained by thermoreflectance mapping, the method is based on a modulation technique relaying on periodic facet temperature modulation induced by pulsed current supply of the laser2. The periodic temperature change of the laser induces variation of the refractive index and consequently modulates probe beam reflectivity. Thermoreflectance technique provides information about real mirror temperature distribution and the absolute value of the temperature is proportional to the signal intensity. The scaling factor is different for different types of lasers and depends on composition and doping of the active region and type of mirror coating. Typically we used micro-Raman spectroscopy to determine the scaling factor for each particular LD3,4. Raman spectroscopy is not sensitive to coating type and gives direct information about absolute temperature. Combining the thermoreflectance and micro-Raman techniques allows us to achieve real temperature maps of the LD mirrors. SAMPLES AND EXPERIMENT The broad-area devices are based on double-barrier separate confinement heterostructures designed for 808 nm emission wavelength. The 15 nm thick tensile strained GaAsP active quantum well (QW) is surrounded by 140 nm thick Al0.3Ga0.7As barrier layers, followed by 150 nm thick Al0.7Ga0.3As outer anti-waveguide layers, which are graded toward the Al0.45Ga0.55As claddings. Thickness of graded layers and cladding layers in both samples was equal to 30 nm and 3 µm respectively. The emitting stripes of about 100 µm width are formed by H+ implantation. The laser facets are asymmetrically co
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