Slide # Goutam Koley Electronic characterization of dislocations MorphologyPotential 0.1 V /Div 10 nm /Div Surf. Potential G. Koley and M. G. Spencer, Appl. Phys. Lett. 78, 2873 (2001)

Slide # Goutam Koley Surface potential patterning using mask UV light 20  m circle quartz mask HFET Sample (35% Al in barrier, 44 nm AlGaN layer)

Slide # Goutam Koley Spatial resolution of charge storage UV exposure through a mask of 1, 2, 5, 10 and 20  m squares Spatial resolution on the order of ~1-2  m 3.5  m G. Koley et al. JAP (2004)

Slide # Goutam Koley Measurements in GaN based transistors AFM scanning probe Biasing Probes

Slide # Goutam Koley Surface morphology and potential profiles in dc biased transistors Gate SourceDrain MorphologySurface Potential Vd = 2V, Vg = -1.5 V

Slide # Goutam Koley Measurement of transients +ve dc bias Probe tip -ve dc bias or square pulse Measurement setup schematic AA 20  resistor AFM scanning probe Biasing Probes Source Gate Drain Gate Drain Source Goutam KoleyG. Koley et al. IEEE Trans. Electron Dev. 50, 886 (2003)

Slide # Goutam Koley Stressed at V g = -12V, V d = 20 V for 2 mins Maximum variation observed ~0.3  m from the gate edge Charges take a long time to reach equilibrium value Potential variation with distance and time 150  m HFET Goutam KoleyG. Koley et al. IEEE Trans. Electron Dev. 50, 886 (2003)

Slide # Goutam Koley Surface conductivity measurements (a) Morphology, (b) conductivity, and (c) overlap of the surface morphology and conductivity images

Slide # Goutam Koley Scanned gate microscopy Scanned gate microscopy is useful to determine the variation of conductivity along a thin channel, and where direct measurement of conductivity is difficult (a) Experimental set up for SGM, (c) the SGM image of a single-walled CNT bundle for V tip = 1 V; Black corresponds to very high resistance.

Slide # Goutam Koley Scanning capacitance microscopy Scanning capacitance technique actually measures the dC/dV signal which is inversely proportional to doping. The advantages of this technique include a large measurement range (10 15 – cm -3 ), and resolution of <10 nm For capacitance measurement a low frequency ac voltage is applied to the sample. The ac voltage periodically changes the tip-sample capacitance. The sensor produces a high frequency signal to measure very small capacitance changes.

Slide # Goutam Koley Application of capacitance microscopy Cross-sectional measurement in a MOSFET under actual operation

Slide # Goutam Koley Applications to GaN samples The dC/dV decreases around the dislocations indicating the reduction in the background carrier concentration Morphology image Capacitance image C-V curve