Deep Defect Relaxation in Hydrogenated Amorphous Silicon: New Experimental Evidence and Implications

1998 ◽  
Vol 507 ◽  
Author(s):  
J. David Cohen ◽  
Fan Zhong ◽  
Daewon Kwon ◽  
C.-C. Chen
Keyword(s):  
Fermi Level ◽  
Emission Rate ◽  
Thermal Emission ◽  
Hydrogenated Amorphous Silicon ◽  
Depletion Region ◽  
Time Resolved ◽  
Apparent Shift ◽  
Hydrogenated Amorphous ◽  
Defect Relaxation ◽  
Thermal Emission Rate

ABSTRACTWe review modulated photocurrent experiments which indicate that thermal emission rate for Do defects in intrinsic samples varies in response to changes in the Fermi-level or quasi-Fermi position. This apparent shift in energy threshold is confirmed using time resolved sub-band-gap spectroscopy. We also demonstrate that such a variation of emission rate with changes in the Fermi-level position, if present within the depletion region near a barrier junction, is consistent with the details of the temperature dependence of the junction capacitance in intrinsic samples.

Exploration of Defect Relaxation Dynamics in Hydrogenated Amorphous Silicon using Temperature Switching Experiments

1994 ◽  
Vol 336 ◽  
Author(s):  
Adam Gardner ◽  
J. David Cohen
Keyword(s):  
Density Of States ◽  
Thermal Emission ◽  
Hydrogenated Amorphous Silicon ◽  
Relaxation Processes ◽  
Relaxation Dynamics ◽  
Temperature Step ◽  
Thermally Activated ◽  
Hydrogenated Amorphous ◽  
Defect Relaxation ◽  
Transient Measurements

ABSTRACTWe have carried out a series of charge transient measurements on a-Si:H in which we insert a double temperature step during the period when electrons are being emitted from deep defects. The behavior of this emitted defect charge is completely inconsistent with any density of states that remains static during the emission; that is, defect relaxation must be invoked. Such measurements allow us to separate the temperature dependence of relaxation from that of thermal emission. In particular, we demonstrate that the emission itself exhibits thermally activated behavior in spite of the ongoing relaxation processes.

Configurational Relaxation of the D Defect in Hydrogenated Amorphous Silicon as a Function of Fermi Energy

1992 ◽  
Vol 258 ◽  
Author(s):  
Thomas M. Leen ◽  
Randall J. Rasmussen ◽  
J. David Cohen
Keyword(s):  
Amorphous Silicon ◽  
Fermi Energy ◽  
Thermal Emission ◽  
Scaling Law ◽  
Hydrogenated Amorphous Silicon ◽  
Dangling Bond ◽  
Universal Scaling ◽  
Depletion Width ◽  
Hydrogenated Amorphous ◽  
Optical Evidence

ABSTRACTBy using light soaking and partial dark annealing to vary the Fermi level in n-type a-Si:H, we have examined the thermal emission of electrons from the dangling bond (D) defect. We find optical evidence for a change in the configuration of the D defect when EF = Ec-0.55±0.08eV. We find that the relaxation rate increases with temperature and increases as EF is brought closer to Ec. Voltage-pulse photocapacitance and depletion-width-modulated ESR show emission is predominantly from D° defects for short emission times and short filling pulse widths. With longer emission times and longer filling pulse widths, emission from D-dominates. We also find that the charge emission transient fits a universal scaling law under a variety of pulsing conditions, temperatures, and anneal states.

Charge and Current Transient Measurements on N-Type Hydrogenated Amorphous Silicon in the Relaxation Regime

1994 ◽  
Vol 336 ◽  
Author(s):  
Uwe W. Paschen ◽  
Daewon Kwon ◽  
J. David Cohen
Keyword(s):  
Thermal Emission ◽  
Depletion Region ◽  
Current Transient ◽  
Relaxation Model ◽  
Si Substrate ◽  
Capacitance Measurements ◽  
Transient Data ◽  
P Type ◽  
Hydrogenated Amorphous ◽  
Transient Measurements

ABSTRACTJunction capacitance measurements were employed to study the thermal emission of electrons after application of a voltage filling pulse on a 80 Vppm PH3 doped a-Si:H sample on p+ c-Si substrate. We show that these data can be explained in terms of the relaxation Model. In addition, the time dependence of the charge flow into the depletion region during the filling pulse is investigated by current transient Measurements. Finally, we present charge transient data for a 9 Vppm a-Si:H sample on n+ c-Si substrate and compare the results to those obtained on samples on p-type substrates.

Identification of the Dominant Electron Deep Trap in a-Si:H: A Critical Test of the Defect Pool vs. Defect Relaxation Pictures

1997 ◽  
Vol 467 ◽  
Author(s):  
Daewon Kwon ◽  
J. David Cohen
Keyword(s):  
Fermi Level ◽  
Thermal Emission ◽  
Deep Trap ◽  
Esr Spectra ◽  
Defect Band ◽  
Large Populations ◽  
Pool Model ◽  
Charged Defects ◽  
Defect Relaxation ◽  
Rule Out

ABSTRACTModulated photocurrent (MPC) measurements in intrinsic a-Si:H reveal a prominent band of electron deep traps with a thermal emission energy near 0.6eV. We have identified this defect band by directly comparing MPC and ESR spectra for both an intrinsic and a lightly n-type doped sample for a various metastable states such that the Fermi level, EF, ranges from less than 0.5eV to more than 0.7eV below Ec. This comparsion unambiguously demonstrates that the MPC band arises from the Do charge state of the defects (specifically, the D−&Do transition). This identification is also confirmed when the quasi-Fermi level is varied by the application of light bias even though the peak emission rate from the MPC defect band is changed by more than a factor of 100. These observations specifically rule out the possibility of large populations of charged defects in intrinsic samples predicted by proponents of the defect pool model. Instead, observed behaviors have a natural explanation in terms of a defect relaxation process.

Sign in / Sign up

Export Citation Format

Share Document