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edfas.org 1 7 ELECTRONIC DEVICE FAILURE ANALYSIS | VOLUME 19 NO. 4 the reference region, L1, and L2. Figure 8(b) shows an sMIM-C image of the “unknown” device. The same three regions of interest are marked with dotted lines and labeled. The image is converted to units of log doping concentration after applying the calibration curve from Fig. 7(c). Figure 8(c) is the average profile extracted from the sMIM-C image in Fig. 8(b). The “reference region” of the “unknown” device has the same doping concentration as step 3 of the calibration sample. The common value allows compensation for the potential offsets that may occur due to system drift or systematic errors during the measurements. The calibration curve doping concentra- tion value is shifted to pass through the reference value on the device sample and then applied to the whole profile to calculate doping concentrations. The comparison of the nominal values with the cali- brated sMIM values shows that the ratio of L1 to L2 is 2.0 for the SIMS and 1.3 for the sMIM, respectively. The result shows that sMIM is sensitive to the doping concentration difference in the two regions, differing by 0.1 log units. The measured values are lower than the SIMS reference values. The authors speculate that the variation can be caused by Fig. 7 Measurement of a GaN epilayer n -type doped staircase. (a) sMIM-C image. (b) Average profile of the alignedimage,withthehighlightsshowingcalibration values. (c) sMIM-C versus doping concentration in log units. The graph shows good linearity over the range of doping and demonstrates the linear relationship of sMIM-C versus log(ND) for a nonsilicon semicon- ductor material. Fig. 8 (a) Cross-sectional schematic of a GaN device. The sample is labeled with nominal doping values independently obtained by SIMS measurement to verify the nominal doping levels before cross sectioning andmeasuringwith sMIM. (b) sMIM image of the “unknown” samplewith color scale converted to n -type doping concentration using the calibration data fromFig. 7. (c) Average profile of the sMIMdata, where the Ref line is highlighted. The 1 × 10 16 region has the same doping concentration as step 3 of the reference sample. (a) (b) (c) (a) (b) (c)