Photoconductor gain mechanisms in GaN ultraviolet detectors

Abstract

GaN photoconductive detectors have been fabricated on sapphire substrates by metal organic vapor phase epitaxy and gas-source molecular beam epitaxy on Si (111) substrates. The photodetectors showed high photoconductor gains, a very nonlinear response with illuminating power, and an intrinsic nonexponential photoconductance recovery process. A novel photoconductor gain mechanism is proposed to explain such results, based on a modulation of the conductive volume of the layer.

Ultrahigh-gain single SnO2 nanowire photodetectors made with ferromagnetic nickel electrodes

“…[26][27][28] Therefore, it is very desirable to understand the mechanism enabling the ultrahigh PC gain obtained here. According to the reports by Binet et al 29 and Muñoz et al, 30 the relationship between the PC gain and the illumination intensity is very informative when considering the underlying mechanism. As shown in Figure 3b, the gain plot (logarithmic) versus intensity shows that there is a turning point in each curve and that the value of the light intensity for the turning point to occur increases with increasing magnetization of the ferromagnetic electrodes.…”

Metal-semiconductor-metal ultraviolet photodetectors based on gallium nitride grown by atomic layer deposition at low temperatures

“…The photoresponse of the devices increases as chopper frequency increases. Trap states-mainly negatively charged Ga vacancies and nitrogen interstitials 22,23 -capture electrons; however, these traps have long relaxation times, i.e.,-electrons remain trapped while holes are mobile longer. As a result, before relaxation occurs, holes continue to contribute to photocurrent.…”

“…As a result, before relaxation occurs, holes continue to contribute to photocurrent. This phenomenon is known as persistent photoconductivity (PPC), 22 resulting in a photoconductive gain. For lower chopping frequencies, the time interval for no-illumination (dark time) is longer, therefore, more traps are relaxed and trapped electrons recombine with holes.…”

“…23 Furthermore, nitrogen-rich GaN favors negatively charged Ga vacancies, which introduce acceptor states as well. 22 Such defect states promote a persistent photoconductive gain that results in increased UV photoresponse.…”

“…The trap states are induced by crystal defects due to nitrogen interstitials. 22,23 Nitrogen interstitials are believed to be responsible for acceptor-like deep trap states. 23 Furthermore, nitrogen-rich GaN favors negatively charged Ga vacancies, which introduce acceptor states as well.…”