Deep Level Transient Spectroscopy Study of Dislocations in SiGe/Si Heterostructures
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0994-F09-04
Deep Level Transient Spectroscopy Study of Dislocations in SiGe/Si Heterostructures Jinggang Lu, Yongkook Park, and George A Rozgonyi Dept of Materials Science and Engineering, North Carolina State University, Raleigh, NC, 27695-7907 ABSTRACT Examination of dislocations in the as-grown and annealed SiGe/Si heterostructures by DLTS indicates the three strong DLTS bands from 70 to 270K in the as-grown sample are likely related to intrinsic point defects or dislocation trails. It was found that a small amount of Fe at dislocations dramatically increases their electrical activity, and the trap concentration due to Fedecorated dislocations can well exceed the total Fe impurities presented along dislocations. Through examining the competitive trapping of Fe at boron and dislocations, it is suggested that Fe trapping only happens at disordered sites along dislocations, such as kinks. INTRODUCTION While clean dislocations are associated with shallow trap levels and exhibit weak electrical activities at room temperatures, after being decorated by impurities, dislocations become strong minority carrier recombination sites and deteriorate device performance. Impurity decoration also makes structural defects less effective for H-passivation. Therefore, knowledge on the electrical activity of dislocations and dislocation-impurity interactions [1] is important for both silicon solar cell and IC device application. In this paper, we examined clean and Fe contaminated dislocations by Deep Level Transient Spectroscopy (DLTS) using a heterostructure SiGe/Si sample. EXPERIMENTAL The SiGe/substrate Si heterostructure used in this study was grown by chemical vapor deposition on a lightly doped p-type Si wafer using either SiH4 or SiH2Cl2 and GeH4 as source gases. The structure consists a 25 nm strained-Si / 1 um Si0.75Ge0.25 / 2 um Si1-xGex graded layer / substrate Si. The Ge concentration change was ~10%/um for the graded layer, giving rise to a misfit dislocation density of 4x109 cm-2. The layer structure was examined in detail by SIMS, CV, and cross-sectional TEM. Fourier-transform DLTS study was performed on as-grown, annealed, Fe contaminated, and phosphorous gettered samples. Iron contamination was realized by dipping the sample in an Fe solution [2] (140ml H2O: 0.6ml NH4OH (29%): H2O2 (32%): 0.1ml Fe spiking solution 1mg Fe/1ml 2% HNO3) for 5 min, rinsing in DI water for 2 min, drying by compressed N2, followed by annealing at 9000C for 30min in Ar in a vertical furnace, and finally quenching in ethylene glycol. P-diffusion gettering was performed by dipping samples in 10% wt phosphorous acid for 1 min and drying with compressed N2, followed by 9000C 40min and 8000C 2h annealing in Ar ambient. Al Schottky diodes were used for DLTS
study of the as-grown and Fe-contaminated samples, while for the p-diffused sample mesa N+P diodes were prepared by wax covering and chemical etching. Coefficient 2 Tw ⎛ 2π ⋅ t ⎞ b1 = ⎟ ⋅ dt was used in all DLTS plots, where TW is the time window for ∫ C (t ) ⋅ sin ⎜ Tw
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