Electrical Properties of Ga2O3:Sn/CIGS Hetero-junction

2014 ◽  
Vol 1603 ◽  
Author(s):  
Kenji Kikuchi ◽  
Shigeyuki Imura ◽  
Kazunori Miyakawa ◽  
Misao Kubota ◽  
Eiji Ohta
Keyword(s):  
Thin Film ◽  
Visible Light ◽  
Dark Current ◽  
Carrier Density ◽  
High Speed ◽  
Depletion Region ◽  
Image Sensors ◽  
Frame Rate ◽  
Semiconductor Layer ◽  
High Quantum Efficiency

ABSTRACTThere is an increased need for highly sensitive imaging devices to develop high resolution and high speed image sensors. Incident light intensity per pixel of image sensors is getting lower because the pixel resolution and frame rate of image sensors are becoming higher. We investigated the feasibility of using a photoconductor with tin-doped gallium oxide (Ga2O3:Sn)/Cu(In,Ga)Se2 (CIGS) hetero-junction for visible light image sensors. CIGS chalcopyrite thin films have great potential for improving the sensitivity of image sensors and CIGS chalcopyrite semiconductors have both a high absorption coefficient and high quantum efficiency. Moreover, the band gap can be adjusted for visible light. We applied Ga2O3 as an n-type semiconductor layer and a hole-blocking layer to CIGS thin film to reduce the dark current. The experimental results revealed that dark current was drastically reduced due to the application of Ga2O3 thin film, and an avalanche multiplication phenomenon was observed at an applied voltage of over 6 V. However, non-doped Ga2O3/CIGS hetero-junction only had sensitivity in the ultraviolet light region because their depletion region was almost completely spread throughout the Ga2O3 layer due to the low carrier density of the Ga2O3 layer. Therefore, we used Ga2O3:Sn for the n-type layer to increase carrier density. As a result, the depletion region shifted to the CIGS film and the cells had sensitivity in all visible regions. These results indicate that Ga2O3:Sn/CIGS hetero-junction are feasible for visible light photoconductors.

Electrical Properties of Photoconductor Using Ga2O3/CuGaSe2 Heterojunction

2013 ◽  
Vol 1538 ◽  
pp. 391-395
Author(s):  
Kenji Kikuchi ◽  
Shigeyuki Imura ◽  
Kazunori Miyakawa ◽  
Misao Kubota ◽  
Eiji Ohta
Keyword(s):  
Visible Light ◽  
Dark Current ◽  
Carrier Density ◽  
Depletion Region ◽  
Image Sensors ◽  
High Quantum Efficiency ◽  
Light Region ◽  
Cigs Thin Film ◽  
Hole Blocking Layer ◽  
High Absorption Coefficient

ABSTRACTThe feasibility of using a photoconductor with a Ga2O3/CuGaSe2 heterojunction for visible light sensors was investigated. CIGS chalcopyrite semiconductors have both a high absorption coefficient and high quantum efficiency. However, their dark current is too high for image sensors. In this study, we applied gallium oxide (Ga2O3) as a hole-blocking layer for CIGS thin film to reduce the dark current. Experimental results showed that the dark current was drastically reduced, and an avalanche multiplication phenomenon was observed at an applied voltage of over 6 V. However, this structure had sensitivity only in the ultraviolet light region because its depletion region was almost completely spread in the Ga2O3 layer since the carrier density of the Ga2O3 layer was much lower than that of the CIGS layer. These results indicate that the Ga2O3/CuGaSe2 heterojunction has potential for use in visible light sensors but that we also need to increase the carrier density of the Ga2O3 layer to shift the depletion region to the CIGS film.

Improved Electrical Properties of Ga2O3:Sn/CIGS Hetero-Junction Photoconductor

2014 ◽  
Vol 1635 ◽  
pp. 83-88
Author(s):  
Kenji Kikuchi ◽  
Shigeyuki Imura ◽  
Kazunori Miyakawa ◽  
Hiroshi Ohtake ◽  
Misao Kubota ◽  
...  
Keyword(s):  
Thin Film ◽  
Quantum Efficiency ◽  
Repetition Rate ◽  
Dark Current ◽  
Carrier Density ◽  
High Efficiency ◽  
Visible Region ◽  
Laser Frequency ◽  
Image Sensors ◽  
High Quantum Efficiency

ABSTRACTWe examined the potential application of CuIn1-xGaxSe1-ySy (CIGS) film for visible light image sensors. CIGS chalcopyrite semiconductors, which are representative of high efficiency thin film solar cells, have both a high absorption coefficient and high quantum efficiency. However, their dark current is too high for image sensors. In this study, we applied gallium oxide (Ga2O3) as a hole-blocking layer for CIGS thin film to reduce the dark current. The dark current of this hetero-junction was 10-9 A/cm2 at less than 7 V. Moreover, an avalanche multiplication phenomenon was observed at an applied voltage of over 8 V. However, this structure had sensitivity only in the ultraviolet light region due to the much lower carrier density of the Ga2O3 layer. We therefore used a tin-doped Ga2O3 (Ga2O3:Sn) layer deposited by pulsed laser deposition (PLD) for the n-type layer to increase the carrier density. The sensitivity of the visible region was observed in the Ga2O3:Sn/CIGS hetero-junction. We also investigated the influence of the laser frequency of the PLD on the transmittance of Ga2O3:Sn and the quantum efficiency of this hetero-junction. Ga2O3:Sn film deposited at a 0.1-Hz laser repetition rate had higher transmittance than at a 10-Hz repetition rate. The Ga2O3:Sn/CIGS hetero-junction also had a higher quantum efficiency with the lower rate (50%) than with the higher rate (30%).

scholarly journals Ultrafast optical imaging technology: principles and applications of emerging methods

Nanophotonics ◽  
2016 ◽  
Vol 5 (4) ◽  
pp. 497-509 ◽  
Author(s):  
Hideharu Mikami ◽  
Liang Gao ◽  
Keisuke Goda
Keyword(s):  
Optical Imaging ◽  
High Speed ◽  
Image Sensors ◽  
Frame Rate ◽  
High Temporal Resolution ◽  
New Class ◽  
Advantages And Disadvantages ◽  
Ultrafast Optical ◽  
Small Field Of View ◽  
Shutter Speed

AbstractHigh-speed optical imaging is an indispensable technology for blur-free observation of fast transient dynamics in virtually all areas including science, industry, defense, energy, and medicine. High temporal resolution is particularly important for microscopy as even a slow event appears to occur “fast” in a small field of view. Unfortunately, the shutter speed and frame rate of conventional cameras based on electronic image sensors are significantly constrained by their electrical operation and limited storage. Over the recent years, several unique and unconventional approaches to high-speed optical imaging have been reported to circumvent these technical challenges and achieve a frame rate and shutter speed far beyond what can be reached with the conventional image sensors. In this article, we review the concepts and principles of such ultrafast optical imaging methods, compare their advantages and disadvantages, and discuss an entirely new class of applications that are possible using them.

A High Performance UV Photodetector from Thin Film Diamond

1995 ◽  
Vol 416 ◽  
Author(s):  
Robert D. Mckeag ◽  
Michael D. Whitfield ◽  
Simon Sm Chan ◽  
Lisa Ys Pang ◽  
Richard B. Jackman
Keyword(s):  
Thin Film ◽  
Visible Light ◽  
Quantum Efficiency ◽  
Dark Current ◽  
External Quantum Efficiency ◽  
High Performance ◽  
Uv Light ◽  
High Sensitivity ◽  
Uv Photodetector ◽  
Deep Uv

ABSTRACTThin film diamond has been used to fabricate a photodetector which displays high sensitivity to deep UV light, with an external quantum efficiency of greater than one, a dark current of less than 0.1nA and which is near ‘blind’ to visible light.

scholarly journals Image Sensors Based on Thin-film on CMOS Technology: Additional Leakage Currents due to Vertical Integration of the a-Si:H Diodes

2006 ◽  
Vol 910 ◽  
Author(s):  
Clement Miazza ◽  
N. Wyrsch ◽  
G. Choong ◽  
S. Dunand ◽  
C. Ballif ◽  
...  
Keyword(s):  
Thin Film ◽  
Amorphous Silicon ◽  
Vertical Integration ◽  
Dark Current ◽  
Cmos Technology ◽  
Image Sensors ◽  
Dark Current Density ◽  
Leakage Currents ◽  
Planar Configuration ◽  
Cmos Chip

AbstractImage sensors based on thin-film on CMOS technology (TFC) have been developed. In this approach, amorphous silicon (a-Si:H) detectors are vertically integrated on top of a CMOS readout chip so as to form monolithic image sensors. In order to reduce as far as possible the dark current density (Jdark) of the TFC sensors, we have focused on analyzing and understanding the behavior of Jdark in this type of detectors. Edge effects along the periphery and at the corners of the pixel, due to the non planar configuration of the vertically integrated photodiodes, are found to be responsible for an increase of the dark current. A new and adapted solution for the minimization of Jdark is proposed, which combines the use of a metal-i-p a-Si:H diode configuration with a deposition on top of an unpassivated CMOS chip. Values of Jdark as low as 12 pA/cm2 at a reverse polarization of V = -1 V are measured on such TFC sensors.

scholarly journals Toward the Ultimate-High-Speed Image Sensor: From 10 ns to 50 ps

Sensors ◽  
2018 ◽  
Vol 18 (8) ◽  
pp. 2407 ◽  
Author(s):  
Anh Nguyen ◽  
Vu Dao ◽  
Kazuhiro Shimonomura ◽  
Kohsei Takehara ◽  
Takeharu Etoh
Keyword(s):  
Temporal Resolution ◽  
High Speed ◽  
Image Sensor ◽  
Image Sensors ◽  
Frame Rate ◽  
Resolution Limit ◽  
Performance Indices ◽  
Theoretical Limit ◽  
Theoretical Derivation ◽  
Trade Offs

The paper summarizes the evolution of the Backside-Illuminated Multi-Collection-Gate (BSI MCG) image sensors from the proposed fundamental structure to the development of a practical ultimate-high-speed silicon image sensor. A test chip of the BSI MCG image sensor achieves the temporal resolution of 10 ns. The authors have derived the expression of the temporal resolution limit of photoelectron conversion layers. For silicon image sensors, the limit is 11.1 ps. By considering the theoretical derivation, a high-speed image sensor designed can achieve the frame rate close to the theoretical limit. However, some of the conditions conflict with performance indices other than the frame rate, such as sensitivity and crosstalk. After adjusting these trade-offs, a simple pixel model of the image sensor is designed and evaluated by simulations. The results reveal that the sensor can achieve a temporal resolution of 50 ps with the existing technology.

Optical properties of photoconductor using crystalline selenium

2014 ◽  
Vol 92 (7/8) ◽  
pp. 645-647 ◽  
Author(s):  
Shigeyuki Imura ◽  
Kenji Kikuchi ◽  
Kazunori Miyakawa ◽  
Misao Kubota
Keyword(s):  
High Resolution ◽  
High Speed ◽  
Metal Electrode ◽  
Image Sensors ◽  
High Quantum Efficiency ◽  
Suitable Material ◽  
Light Region ◽  
Highly Sensitive ◽  
Photosensitive Layer ◽  
High Absorption Coefficient

Recently, there has been an increased need for highly sensitive solid-state imaging devices to develop high-resolution and high-speed image sensors. Crystalline selenium is a suitable material for a photosensitive layer because of its high absorption coefficient in the visible light region. In our experiment with an image pick-up tube using crystalline selenium as a photosensitive layer, a high-resolution image was obtained for the first time. In addition, test sandwich cells have been fabricated to demonstrate a large photocurrent multiplication phenomenon with very high quantum efficiency greatly exceeding unity as a result of injection carriers from an external electrode caused by a high electric field at the interface between the crystalline selenium and the metal electrode.

Image Sensors in Tfa Technology - Status and Future Trends

1998 ◽  
Vol 507 ◽  
Author(s):  
M. Böhm ◽  
F. Blecher ◽  
A. Eckhardt ◽  
K. Seibel ◽  
B. Schneider ◽  
...  
Keyword(s):  
Thin Film ◽  
Spectral Sensitivity ◽  
Dark Current ◽  
Transient Behavior ◽  
Image Sensors ◽  
Cell Design ◽  
Future Trends ◽  
Temperature Influence ◽  
Future Perspectives ◽  
Research Results

ABSTRACTImage sensors in TFA (Thin Film on ASIC) technology have been successfully fabricated and tested. This paper provides a survey of TFA research results so far and outlines future perspectives. The properties of different a-Si:H b/w and color thin film detectors are evaluated, including spectral sensitivity, dark current, temperature influence and transient behavior. Furthermore several TFA prototypes and emerging concepts are presented, ranging from a simple one-transistor cell design to a locally autoadaptive sensor.

Amorphous Silicon Image Sensor Arrays

1992 ◽  
Vol 258 ◽  
Author(s):  
M J Powell ◽  
I D French ◽  
J R Hughes ◽  
N C Bird ◽  
O S Davies ◽  
...  
Keyword(s):  
Amorphous Silicon ◽  
High Speed ◽  
Dynamic Range ◽  
Sensor Arrays ◽  
Image Sensor ◽  
Low Noise ◽  
Image Sensors ◽  
Frame Rate ◽  
Intimate Contact ◽  
Current Densities

ABSTRACTWe have developed a technology for 2D matrix-addressed image sensors using amorphous silicon photodiodes and thin film transistors. We have built a small prototype, having 192×192 pixels with a 20μm pixel pitch, and assessed its performance. The nip photodiodes can have dark current densities of less than 1011 A.cm-2 (up to 5V reverse bias) and peak quantum efficiencies of 88% (at 580nm). We operated the sensor in real time mode at high speed (50 Hz frame rate and 64μS line time). The image sensor has a low noise performance giving a dynamic range in excess of 104. The maximum crosstalk is about 2%, which allows at least 50 grey levels. The bottom contact of the photodiode acts as a light shield from light through the substrate, which enables the sensor to be operated as an intimate contact image sensor to image a document placed directly on top of the array. In this mode, the CTF was 75% at 2 lp.mm1. Good quality images are demonstrated in both front projection and intimate contact imaging modes.

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