Photo-Hall effect spectroscopy with extended illumination in p-type semiconductors as a tool for deep level detection, and negative differential photoconductivity study
Abstract
detection and optoelectronics. Despite good solidification properties, the material suffers from the thermal instability; deep level (DL) assisted recombination and polarization.
Existing thermal emission spectroscopy methods have known limitations. DL properties determined by them may differ from those established at room temperature.
In this work, we report on a more elaborated photo-Hall effect spectroscopy (PHES) excited by the intensive white laser illumination filtered with a monochromator. PHES allows us the determination of the position of DLs inside the band gap by analyzing the Hall mobility (µH) and photoconductivity (PhC) changes as a result of monochromatic light excitation.
Whenever the photon energy meets the respective trap threshold energy (ET), free holes or electrons are generated by the light and one may observe a characteristic onset of µH and PhC, see Fig. 1. The increase of the mobility with a positive sign of the Hall voltage (VH) indicates the DL with ET>EF (energy counts from the valence band).
The decrease of µH by prevailing electron generation accordingly indicates the DL with ET<EF, see Fig. 1 (b). The following DLs were discovered using PHES: ET1 = Ev + 0.62 eV, ET2 = Ev + 0.71 eV, ET3 = Ec - 1.0 eV, and ET4 = Ec - 1.3 eV.
Differential negative photoconductivity (NDPC) can be observed in the energy region 1.2-1.3 eV and explained by developed DL model. Experimental data obtained by dynamical and steady state PHES were completed by Shockley-Read-Hall charge dynamic model simulation solved by Runge-Kutta method.
The study also presents mobility measurements of the dominant and minority carriers. This approach can be used to characterize the detection properties of the material.