Enhanced image sensing with avalanche multiplication in hybrid structure of crystalline selenium photoconversion layer and CMOSFETs

Abstract

The recent improvements of complementary metal–oxide–semiconductor (CMOS) image sensors are playing an essential role in emerging high-definition video cameras, which provide viewers with a stronger sensation of reality. However, the devices suffer from decreasing sensitivity due to the shrinkage of pixels. We herein address this problem by introducing a hybrid structure comprising crystalline-selenium (c-Se)-based photoconversion layers and 8 K resolution (7472 × 4320 pixels) CMOS field-effect transistors (FETs) to amplify signals using the avalanche multiplication of photogenerated carriers. Using low-defect-level NiO as an electric field buffer and an electron blocking layer, we confirmed signal amplification by a factor of approximately 1.4 while the dark current remained low at 2.6 nA/cm2 at a reverse bias voltage of 22.6 V. Furthermore, we successfully obtained a brighter image based on the amplified signals without any notable noise degradation.

Formation of Micro‐Patterned Ga2O3/Se Heterojunction and its Application to Highly Sensitive Avalanche Photodiode

“…Conversely, Ga 2 O 3 /Se heterojunction devices exhibit a typical tendency of avalanche multiplication in the J – V curve shown in Figure 5a. [ 14,34 ] Ga 2 O 3 /Se heterojunction devices showed small photocurrents under zero‐bias conditions; however, a rise in photocurrent was observed when the reverse bias voltages increased over 10 V.…”

“…Because the re‐evaporation, pinholes, and peeling off from the beneath layer were caused by increasing residual stress during the thermal crystallization of Se thin films, a thin Te layer (<1 nm) was inserted below the Se layer to increase the adhesion of Se to the window layers. [ 3,4,6,7,14,15,32 ] 5) Thermal evaporation of the MoO 3 hole transfer layer (HTL) and Au bottom electrode: 6) Patterning of the Au electrode: Au electrodes were patterned with an iodine‐based etchant. 7) Plasma etching of Se and MoO 3 layers: MoO 3 and Se layers were etched through Au patterns as etching masks using O 2 plasma etching at a flow rate of 30 sccm for O 2 and radio frequency (RF) power of 300 W for 3 min.…”

“…Because the re-evaporation, pinholes, and peeling off from the beneath layer were caused by increasing residual stress during the thermal crystallization of Se thin films, a thin Te layer (<1 nm) was inserted below the Se layer to increase the adhesion of Se to the window layers. [3,4,6,7,14,15,32] 4 and Table 1 show the photographs of the fabricated Ga 2 O 3 /Se micro-PD and the thickness of each layer, respectively.…”

“…[11][12][13] Recently, Imura reported a Se thin-film photoelectric conversion layer on a CMOS circuit for next-generation 8 K super-high vision image sensors with high responsivity over the entire visible-wavelength range. [14] A Ga 2 O 3 wide bandgap n-type layer and NiO layer were used as a hole-blocking layer and electron-blocking layer in a Ga 2 O 3 /Se/NiO heterojunction, respectively. [15] Because Ga 2 O 3 has attractive features for applications in n-type window layers of APD such as widegap and direct transition bandgap, it has been applied to thin-film-based solar-blind APD by combining with GaN or SiC.…”

Technological Evolution of Image Sensing Designed by Nanostructured Materials

“…Hybrid image sensors have shown a number of intriguing performance features by exploiting different aspects of non-Si photoconversion films such as high LDR, global shutter type, and high near-infrared(NIR) and X-ray sensitivity. The formation of a brighter image with enhanced signals and clear noise deterioration is shown in Figure …”