D. W. Kang

Optical subthreshold current method for extracting the interface states in MOS systems

Optical subthreshold current method (OSCM) is proposed for characterizing the interface states in MOS systems using the current-voltage characteristics under a photonic excitation. An optical source with a subbandgap (E/sub ph/<E/sub g/) photonic energy (E/sub ph/=0.943 eV, P/sub opt/=+5 dBm), which is less than the silicon bandgap (E/sub g/=1.12;eV), is employed for the optical subthreshold current characterization of interface states in the photoresponsive energy band. We applied the OSCM method under a subbandgap photonic excitation to MOS systems with a poly-Si gate and verified a U-shaped distribution of interface trap density D/sub it/=10/sup 10//spl sim/10/sup 12/ eV/sup -1/cm/sup -2/ for n- and p-type MOSFETs with W/L=30 /spl mu/m/1.2 /spl mu/m.

Deep-depletion high-frequency capacitance-voltage responses under photonic excitation and distribution of interface states in MOS capacitors

Probing the deep-depletion mode high-frequency capacitance-voltage (C-V) responses of MOS capacitors under photonic excitation, the distribution (D/sub it/) of the interface states (E/sub t/) at Si/SiO/sub 2/ heterojunctions was characterized. A photon energy E/sub ph/=0.943 eV (less than the silicon energy bandgap) was employed for the characterization of interface states in the photoresponsive energy band. In order to limit the photonic contribution to the change in the gate capacitance by excess carriers excited only from the interface states, a fast dc sweep rate (50 mV/s) with a high-frequency (500 kHz) small-signal was applied. Photonic C-V responses with a slow dc sweep for E/sub ph/=0.943 eV and a fast sweep for E/sub ph/=1.481 eV have been also provided for a comparison. Modulating the surface potential with the gate bias, a U-shaped distribution of D/sub it/ was obtained over the photoresponsive energy band in (E/sub C/-E/sub ph/)<E/sub t/<(E/sub i/-q/spl phi//sub f/+q/spl phi//sub s/) from NMOS and (E/sub i/+q/spl phi//sub s/-q/spl phi//sub f/)<E/sub t/<(E/sub V/+E/sub ph/) from PMOS capacitors. D/sub it,max/ was observed to be /spl sim/1.76/spl times/10/sup 11/ cm/sup -2/eV/sup -1/ on the edges of conduction and valence bands.

Distribution of Interface States in MOS Systems Extracted by the Subthreshold Current in MOSFETs under Optical Illumination

Sentence (p. 874) in Chapter II starting with “They are ⋯ on the device fabrication process [10-15].” should be corrected as “They are ⋯ on the device fabrication process [10-15]. We also note that charge states in traps are gate bias-dependent [16].”.Two paragraphs (p. 874) in Chapter II “Figure 2 shows the energy-band diagram ⋯ the gate voltage applied across the MOS capacitor.” and “Figure 3(c) shows the condition at inversion in which there is now a net negative charge in the acceptor states [15,16].” and Figs. 2 and 3 should be removed.