Single Shockley faults evolution under UV optical pumping
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1246-B03-06
Single Shockley faults evolution under UV optical pumping
Andrea Canino1, Massimo Camarda1, Antonino La Magna1 and Francesco La Via1 1 Consiglio Nazionale delle Ricerche, Istituto di Microelettronica e Microsistemi CNR IMM, Z.I. VIII Strada 5 I 95121 Catania, Italy
ABSTRACT Single Shockley faults (SSF) have been studied in 4H-SiC epitaxial layers by using a spatially-resolved micro-photoluminescence technique. In particular the effect of the UV pumping laser has been investigated. Samples have been irradiated at different power densities (PDs) in order to find a threshold for the growth of the SSF defects. A low power density (115 W/cm2) exposition at 325 nm does not affect the structural properties of the epitaxial layers. We observed a growth of this defect through the epitaxial layers when the power density is increased over the value of 230 W/cm2 and the formation of new SSF for power density higher than 290 W/cm2. INTRODUCTION 4H-SiC, due to its superior structural, electrical and mechanical properties, is an interesting material for the development of devices with improved performances in the field of high-power and high-frequency electronics and also for high-temperature applications [1]. The limiting step for the commercialization of efficient bipolar devices is the degradation of I-V characteristics due to the presence of stacking faults (SFs) in the epitaxial layers [2]. A spatially-resolved micro-photoluminescence (mPL) technique has been used to individuate SFs that exhibit an intense room temperature photoluminescence (PL) signal [3-6]. This is a powerful method to obtain both density and geometry of SFs but it implies an interaction with the samples due to the high power density used to realize the maps. We focused our attention on the effect of the pumping laser on the single Shockley fault, considered the responsible of degradation of bipolar devices, that has a PL peak centered, at room temperature, at about 2.93 eV. In fact it is known that high e-h pairs density (due to current or due to high power optical pumping) can supply the energy for the enlargements and formation of SSFs [2][5][6]. mPL maps of the sample surface have been performed with a PD of about 115 W/cm2 in order to individuate and analyze the SSFs [6]. A particular experimental setup has been used to vary the power density in the 115÷800 W/cm2 range. EXPERIMENT The sample used for the analysis have been growth on a 8° off axis SiC substrate cut
towards the [11-20] direction by using trichlorosilane as precursor gas [7]. Two different growth rates (GR) have been used to realize the samples: a high GR (112 µm/h) and a low GR (12 µm/h). The samples have been thinned after growth to a thickness of about 3 µm in order to allow to the pumping laser arriving at the interface between the substrate and the epitaxial layer. PL measurements have been performed by using a LabRAM HR 800 by Horiba Jobin Yvon. The apparatus allows performing spectral analysis on samples and spatially resolved PL intensity maps at a fixed wavelengt
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