Electron trapping kinetics at dislocations in relaxed Ge0.3Si0.7/Si heterostructures

Abstract

The capture kinetics and trapping properties of a dislocation related electron trap detected in strain-relaxed, compositionally graded Ge0.3Si0.7/Si grown by rapid thermal chemical-vapor deposition are investigated by deep-level transient spectroscopy (DLTS). The volume DLTS trap concentration scales linearly with the areal threading dislocation density, as determined by electron-beam-induced current measurements on samples with different compositional grading rates, indicating that the detected trap is most likely associated with dislocation core states in these graded structures. The dislocation related trap exhibits both the logarithmic dependence of DLTS peak height on fill pulse time tp, and broadened DLTS peaks which typically characterize carrier trapping at dislocations. These effects are quantified and analyzed to gain insight into the trapping properties of dislocations in GeSi/Si heterostructures and to investigate the effects of dislocation related carrier trapping on DLTS measurements. It is demonstrated that the peak broadening, as characterized by the dimensionless broadening parameter FWHM/Tp, where FWHM and Tp are the full width at half-maximum of the DLTS peak and the DLTS peak temperature, respectively, monotonically decreases with decreasing fill pulse duration, and approaches point-defectlike behavior for tp<100 μs. The observed broadening is asymmetric about Tp, and occurs predominantly on the low-temperature side of the DLTS peak. This asymmetric broadening is shown to shift the ‘‘apparent’’ trap activation energy, as determined by Arrhenius analysis, from EC−0.6 eV to EC−0.9 eV (relative to the bulk conduction-band edge) as tp decreases from 5 ms to 50 μs. These observations are explained by the presence of a dislocation related distribution of energy levels within the GeSi band gap and the consequent fill-pulse-dependent local band bending. The lowest-energy states within this distribution are preferentially filled with electrons for short fill pulse times. The Arrhenius-determined ‘‘apparent’’ activation energy is hence interpreted as being a measure of the average energy of the filled defect states, weighted by the density of states distribution in this energy band and by the related fill-pulse-dependent local band bending. It is further demonstrated that the minority-carrier capture cross section may be enhanced by the presence of an attractive coulombic barrier for minority carriers at the dislocations, and we use the logarithmic capture equations to derive a value of 4×10−12 cm2 for this ‘‘effective’’ capture cross section.

Influence of dislocations in strained Si∕relaxed SiGe layers on n+∕p-junctions in a metal-oxide-semiconductor field-effect transistor technology

“…3͒ yields an estimated capture cross section of 9.6ϫ 10 −13 cm 2 , a result in good agreement with literature. 13 The increased leakage in SiGe virtual substrates can be problematic in MOSFET technologies for two reasons: ͑1͒ Higher leakage will add to the total power consumption per chip, increasing self-heating problems even more than in standard silicon technologies and ͑2͒ Dislocations can deteriorate the characteristics of single transistors, potentially causing the transistor to fail in its operation.…”

Deep level transient spectroscopy study of the effect of Mn and Bi doping on trap formation in ZnO

“…This gives rise to variations both in Ea and the capture cross-section (σ) of the defect [33]. Thus electron capture into an extended defect causes a Coulombic barrier to evolve with time, and the DLTS signal will therefore show dependence on the fill pulse time (t F ) according to [34]:…”

Dislocation related defect states in GaN irradiated with 1 MeV electron‐beam

“…In case of noninteracting point defect, the defect density has exponential relation with filling pulse width. However, in case of point defects arranged around a TD, the defect density has logarithmic relation with filling pulse width [8][9][10][11]. Figure 3(a) shows a comparison of the DLTS spectra of sample B before and after 1-MeV electron beam irradiation.…”

“…o C. The current and irradiation time of electron beam were 0.48 mA and 534 sec.The Monte Carlo simulations for the electron trajectory energy of 1-MeV were done to produce defects in the depletion region in GaN layer [8]. For DLTS measurement, Shottky diodes were prepared by evaporating Au contacts, and then Al ohmic contacts were fabricated.…”