Metal-oxide-semiconductor tunneling photodiodes with enhanced deep depletion at edge by high-k material

Abstract

Metal-oxide-semiconductor (MOS) photodetector with the high-k material enhanced deep depletion at edge was demonstrated. The mechanism of saturated substrate injection current in MOS capacitor was adopted. By building HfO2 based devices that with the direct observation of the enhanced edge charge collection efficiency due to fringing field effect in inversion, we are able to show a photodetector with 3000 times (ratio of photocurrent to dark current) improvement in sensitivity than the conventional SiO2 based tunneling photodiodes (approximate 100 times) in the visible.

Edge field enhanced deep depletion phenomenon in MOS structures with ultra-thin gate oxides

“…The critical field analysis suggests that the edge field dominates the C-V curve behavior until the bulk start to go into deep depletion region. The field ratio between edge and bulk for HfO 2 /SiO 2 is 1.21 as shown in Fig 5. The result is consistent to the previous study that the deep depletion occurs earlier in HfO 2 /SiO 2 than in SiO 2 due to enhanced edge field by high-k material [3].…”

“…The tunneling induced deep depletion expansion-shrinkage has been enhanced by the edge field of abrupt junction in the MOS structure during illumination [3] as shown in Fig.1 of the SiO 2 and HfO 2 devices. …”

“…Liang et al demonstrated that deep depletion can be induced by minority carriers tunneling away from the substrate and tunneling current in ultra-thin gate oxide (<40 Å) [4]. Cheng et al demonstrated that the high-k oxide has much less uniformity in the interface than conventional SiO 2 device, which leads to high-k oxide has deeper depletion region in the non-uniform region than in ultra-thin SiO 2 [3,5]. Deep depletion in MOS structure is so far of use for the characterization of the interface properties.…”

“…The previous research shows that the edge fringing field effect greatly degrade tunnel oxide quality especially after electrons programming in charge trapping (CT) NAND Flash [2]. Besides, the depletion width at the MOS device's edge was enhanced by the edge fringing field effect and the phenomenon was taken into consideration of the design of Perimeter Light Absorption (PLA) type MOS tunneling photodiode [3]. However, studies on the relationships between edge enhanced deep depletion phenomena and current-voltage, capacitance-voltage behavior are quite few.…”

Photo-induced tunneling currents in MOS structures with various HfO2/SiO2 stacking dielectrics

“…Additionally, it is noticed that the inversion current of MOS photodiode with specific perimeter dependency was reported. 23,24 However, in this work, it was found that the I-V characteristic of sample 3H shows area but not perimeter dependency when measured under illumination with high intensity. Current conduction mechanism was also proposed for this observation.…”