LED(PN Diode) 측정 및 분석 실습 Report

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1. PN junction diode (LED)

LED는 전자가 많아 음의 성격을 띤 n형 반도체와 전자의 반대 개념인 정공이 많아 양의 성격을 띤 p형 반도체의 이종접합 구조를 가진다. Forward bias를 가하면 전류가 흘러 발광을 하며, 에너지 준위차인 Band gap에 따라 빛의 색상이 정해진다. LED의 I-V 특성에서는 Forward bias 시 Threshold Voltage 이하에서 전류가 거의 흐르지 않다가 Vth 이상이 되면 전류가 급격히 증가하며, Reverse bias 시 Breakdown voltage까지는 전류가 거의 0이 되다가 그 이상에서 급격히 증가하는 Avalanche breakdown 현상이 발생한다.
2. Photocurrent

LED 소자에 빛을 가하면 Band Gap보다 큰 에너지를 가지는 Photon에 의해 전자-정공쌍이 생성되어 광전류가 흐르게 된다. LED의 Response Speed는 입력 전류 파형에 대해 빛을 내보내는데 발생하는 시간 지연으로, Rise time과 Decay time으로 정의된다. 또한 PPC(Persistent Photoconductivity) effect는 빛 조사 후 암전류로 돌아오지 않고 전도성이 유지되는 현상으로, 전자-정공쌍이 Oxygen Vacancy에 Trap되어 재결합이 늦어지면서 발생한다.
3. 4-point measurement

4-point probe method는 전도성 박막 및 실리콘 웨이퍼 등의 Sheet Resistance를 측정하는데 널리 사용되며, 4개의 탐침을 시료 표면에 접촉시켜 전류를 흘리고 전압을 측정하여 저항을 구한다. TLM(Transmission Line Method)을 통해 Contact Resistance와 Channel Resistance를 분리하여 측정할 수 있다.

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1. PN junction diode (LED)

PN junction diodes, including light-emitting diodes (LEDs), are fundamental semiconductor devices that play a crucial role in modern electronics and optoelectronics. The PN junction is formed by the interface between p-type and n-type semiconductor materials, which creates a depletion region with an electric field. When a forward bias is applied, electrons and holes are injected into the depletion region, leading to the recombination of charge carriers and the emission of photons. This principle is the basis for the operation of LEDs, which are widely used in various applications such as displays, lighting, and signaling. The unique properties of PN junction diodes, including their rectifying behavior, light emission, and ability to control the flow of current, make them indispensable components in a wide range of electronic circuits and devices. Understanding the fundamental principles of PN junction diodes is essential for designing and optimizing these devices for diverse applications in the fields of electronics, optoelectronics, and photonics.
2. Photocurrent

Photocurrent is a fundamental concept in optoelectronics and photovoltaics, describing the electrical current generated by the absorption of photons in a semiconductor or photodetector device. When photons with sufficient energy are absorbed by a semiconductor material, they can excite electrons from the valence band to the conduction band, creating electron-hole pairs. These charge carriers are then separated by an electric field or a built-in potential, resulting in the flow of photocurrent. The magnitude of the photocurrent is directly proportional to the intensity of the incident light and the efficiency of the photodetector in converting photons into electrical signals. Photocurrent is a crucial parameter in the design and operation of various optoelectronic devices, such as photodiodes, phototransistors, and solar cells, as it determines the sensitivity, responsivity, and overall performance of these devices. Understanding the principles of photocurrent generation and its dependence on factors like wavelength, light intensity, and device structure is essential for the development and optimization of advanced optoelectronic systems in fields like imaging, sensing, and renewable energy.
3. 4-point measurement

The 4-point measurement, also known as the Kelvin or van der Pauw method, is a powerful technique used to accurately measure the electrical properties of materials, particularly thin films and semiconductor samples. This method involves the use of four probes or electrodes placed in contact with the sample, with two probes used to apply a current and the other two probes used to measure the resulting voltage drop. By separating the current and voltage measurement, the 4-point method eliminates the effects of contact resistance and lead resistance, providing a more accurate measurement of the intrinsic electrical properties of the material, such as resistivity, sheet resistance, and carrier concentration. This technique is widely used in the characterization of semiconductor materials, thin films, and other electronic materials, as it allows for the precise determination of key parameters that are crucial for device design, process optimization, and quality control. The 4-point measurement is an essential tool in the field of materials science and semiconductor technology, enabling researchers and engineers to gain a deeper understanding of the electrical behavior of materials and to develop more efficient and reliable electronic devices.