Conditions for a carrier multiplication in amorphous-selenium based photodetector

Abstract

Amorphous selenium is a promising candidate for high sensitivity photodetector due to its unique carrier multiplication phenomenon. More than 10 carriers can be generated per incident photon, which leads to high photo-conversion efficiency of 1000% that allows real-time imaging in dark ambient. However, application of this effect has been limited to specific devices due to the lack in material characterization. In this article, mechanism of carrier multiplication has been clarified using time-of-flight secondary ion mass spectroscopy and Raman spectroscopy. A prototype photodetector achieved photo conversion efficiency of 4000%, which explains the signal enhancement mechanism in a-Se based photodetector.

High sensitivity photodetector made of amorphous selenium and diamond cold cathode

“…In addition, the I-V curve at voltage 100-350 V shows a relatively small current increase, while it shifts to a rapid increase at voltages above 350 V. This tendency in the I-V curve suggests that there are two or more factors that limit the I-V characteristics. A possible explanation is that the emission current is limited by transport of photogenerated holes at voltages lower than 350 V, then it shifts into "avalanche mode" when the applied voltage is above 350 V. In our previous study, carrier multiplication at applied voltage around 340 V is reported for a 2 m thick film in a contact current -applied voltage measurement [7].…”

“…A lightly N-doped diamond with extraction voltage of 400 V was selected in this study, to apply high voltages of up to 350 V between the anode and the cathode. This high voltage was necessary to induce carrier multiplication in a-Se [7].…”

“…a-Se samples were annealed for 5 min at each temperature, which was an optimal condition proposed in our previous study [12]. A detailed characterization of the structure and electronic properties of the films are presented elsewhere [7,12].…”

“…The advantages of vacuum-type devices are vacuum insulation and its extremely low dark current, as well as potentially wide dynamic range. Recently, high-sensitivity photodetection has been demonstrated using arsenic-incorporated a-Se as a photoconductive anode and N-doped diamond as a cold cathode [7,8]. The use of nitrogen (N)-doped diamond, in which urea is used as a dopant, should provide stable electron emission utilizing a negative electron-affinity surface.…”

Amorphous selenium (a-Se) based wide wave-range photodetector driven by diamond cold cathode

“…With a negative electron affmity surface and M-I-V type emission [3], N-doped diamond emitter should provide sufficient emission current for wide dynamic range, as well as small dispersion angle for high spatial resolution. Furthermore, high-sensitivity photo detection has been demonstrated using carrier multiplication in a-Se [4]. Emission current-applied voltage (I V) characteristics of the detector are compared between photodetectors with different set-up configurations in order to evaluate the sensitivity enhancement due to internal signal multiplication.…”