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Related Concept Videos

Non-ohmic Devices00:51

Non-ohmic Devices

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In most substances, the current flow is proportional to the voltage applied to it. A simple relationship between the values of current, voltage, and resistance is known as Ohm's law. Nonohmic devices do not exhibit a linear relationship between voltage and current. One such device is the semiconducting circuit element known as a diode. A diode is a circuit device that allows current flow in only one direction.
Consider a simple circuit consisting of a battery, a diode, and a resistor. A...
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Zener Diodes01:16

Zener Diodes

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Zener diodes are specialized semiconductor devices designed to operate in the reverse breakdown region, where they allow current to flow into the cathode, making it positive relative to the anode. This reverse operation distinguishes Zener diodes from conventional diodes and enables their use in various applications, most notably as voltage regulators. One of the defining characteristics of Zener diodes is their nearly vertical I-V (current-voltage) characteristic curve above a certain...
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Metal-Semiconductor Junctions01:24

Metal-Semiconductor Junctions

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The contact of metal and semiconductor can lead to the formation of a junction with either Schottky or Ohmic behavior.
Schottky Barriers
Schottky barriers arise when a metal with a work function (Φm) contacts a semiconductor with a different work function (Φs). Initially, electrons transfer until the Fermi levels of the metal and semiconductor align at equilibrium. For instance, if Φm > Φs, the semiconductor Fermi level is higher than the metal's before contact. The...
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Biasing of Metal-Semiconductor Junctions01:27

Biasing of Metal-Semiconductor Junctions

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Biasing metal-semiconductor junctions involves applying a voltage across the junction. Specifically, the metal is connected to a voltage source, while the semiconductor is grounded. This technique is essential for controlling the direction and magnitude of current flow in electronic devices, including diodes, transistors, and photovoltaic cells.
In Schottky junctions, where the semiconductor is n-type, applying a positive voltage to the metal relative to the semiconductor reduces its Fermi...
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Biasing of P-N Junction01:16

Biasing of P-N Junction

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The operation of a p-n junction diode involves various biasing conditions, including forward bias, reverse bias, and equilibrium.
In equilibrium, no external voltage is applied across the p-n junction. The depletion region is formed at the junction interface due to the diffusion of carriers, which leaves behind charged dopants, acceptors on the p-side, and donors on the n-side. These immobile charges create an electric field that prevents further diffusion of carriers. The related energy band...
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P-N junction01:11

P-N junction

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A p-n junction is formed when p-type and n-type semiconductor materials are joined together. At the interface of the p-n junction, holes from the p-side and electrons from the n-side begin to diffuse into the opposite sides due to the concentration gradient. This diffusion of carriers leads to a region around the junction where there are no free charge carriers, known as the depletion region. The charge density within the depletion region for the n-side and p-side can be described by the...
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Related Experiment Video

Updated: Oct 8, 2025

Synthesis and Characterization of High c-axis ZnO Thin Film by Plasma Enhanced Chemical Vapor Deposition System and its UV Photodetector Application
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Low-Operating-Temperature NO2 Sensor Based on a CeO2/ZnO Heterojunction.

Kai Sun1, Guanghui Zhan1, Hande Chen2

  • 1State Key Laboratory of Marine Resource Utilization in South China Sea, School of Materials Science and Engineering, Hainan University, Haikou 570228, China.

Sensors (Basel, Switzerland)
|December 28, 2021
PubMed
Summary
This summary is machine-generated.

New CeO2/ZnO heterojunction nanorod sensors offer high sensitivity and selectivity for nitrogen dioxide (NO2) detection at low operating temperatures, even at room temperature.

Keywords:
CeO2NO2 detectiongas sensorheterojunctionlow operating temperature

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Synthesis and Characterization of High c-axis ZnO Thin Film by Plasma Enhanced Chemical Vapor Deposition System and its UV Photodetector Application
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Area of Science:

  • Materials Science
  • Chemical Engineering
  • Sensor Technology

Background:

  • Chemiresistive sensors are crucial for gas detection.
  • Low-operating-temperature sensors are desirable for energy efficiency and safety.
  • Nitrogen dioxide (NO2) is a common air pollutant requiring sensitive detection methods.

Purpose of the Study:

  • To develop and characterize CeO2/ZnO heterojunction nanorod-array based chemiresistive sensors.
  • To evaluate their gas-detecting performance at low operating temperatures.
  • To understand the mechanism behind enhanced gas sensitivity.

Main Methods:

  • Synthesis of CeO2/ZnO heterojunction nanorod arrays via anodic electrodeposition coating and hydrothermal treatment.
  • Fabrication of chemiresistive sensors using the synthesized nanorod arrays.
  • Testing sensor response and selectivity to NO2 and interfering gases at various temperatures (120 °C and room temperature).

Main Results:

  • The CeO2/ZnO heterojunction sensor exhibited significantly higher sensitivity to NO2 at 120 °C compared to pure ZnO.
  • The sensor showed a linear and rapid response to NO2 even at room temperature (25 °C).
  • Exceptional selectivity was observed, with a substantially lower response to interfering gases than to NO2.

Conclusions:

  • The CeO2/ZnO heterojunction structure enhances gas-sensing performance at low temperatures.
  • The built-in field at the heterojunction provides additional carriers for ZnO, improving adsorption.
  • These findings highlight the potential of CeO2/ZnO heterojunctions for efficient low-temperature NO2 detection.