Photoresponses in polycrystalline silicon phototransistors incorporating germanium quantum dots in the gate dielectrics

Abstract

Polycrystalline silicon (poly-Si) thin-film transistors (TFTs) incorporating germanium (Ge) quantum dots (QDs) in the gate oxide were fabricated as efficient blue to near ultraviolet phototransistors for light detection and amplification. Under 405–450 nm light illumination, Ge QDs poly-Si TFTs exhibit not only strong photoresponses in the drive current but also much improved subthreshold characteristics than that measured in darkness. This originates from the fact that only photoexcited holes within Ge QDs are injected into the active channel via vertical electric field and contribute excess mobile carriers for photocurrent but without the associated photogenerated electron induced junction barrier lowering.

Formation of Ge quantum dots array in layer-cake technique for advanced photovoltaics

“…In fact, not only the QD size, shape, and crystalline structure, but also the surface traps of QDs would correlate with the observed photoluminescence. In addition, our previous work on Ge QD MIS photodetectors [12] and phototransistors [13] have demonstrated a considerable blue-shift in the peak energies of the spectral photoresponsivity as the Ge dot size decreases from 9 to 5 nm, suggesting that the light absorption originates from the QCEs of the Ge QDs.…”

Designer germanium quantum dot phototransistor for near infrared optical detection and amplification

“…Our previous report demonstrated Ge-nanocrystallite phototransistors for blue to near ultraviolent (400-550 nm) photodetection based on a double-gated poly-Si thin-film transistor (TFT) structure [23,24]. In these Ge-nanocrystallite photo-TFTs, self-assembled clusters of 7.62 ± 0.94 nm, irregular-shaped Ge nanocrystallites were embedded within a 45 nm thick gate oxide.…”

“…In these Ge-nanocrystallite photo-TFTs, self-assembled clusters of 7.62 ± 0.94 nm, irregular-shaped Ge nanocrystallites were embedded within a 45 nm thick gate oxide. External quantum efficiency as high as >200% is achieved from these doubled-gated Ge-nanocrystallite photo-TFTs under 400-550 nm illumination, yet the on-off current ratio (I on /I off ) of 10 4 and the transient speed, which is of the sub-millisecond [24], need to be further improved. Recently, we have demonstrated a unique capability to precisely place spherical Ge quantum dots (QDs) of desired sizes at targeted spatial locations over the Si substrate using selective oxidation of lithographically-patterned SiGe nano-pillars over buffer Si 3 N 4 layers on the Si substrate [25].…”

Miniband-Resonant-Tunneling Optoelectronic Device

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