We know that the primary function of an LED chip is to convert electricity directly into light, making it the heart of an LED. This article briefly introduces the basics of LED chips, including their classification, structure, characteristics, and important parameters. The LED chip is the core component of the semiconductor light-emitting device, the LED (Light Emitting Diode). The principle of LED light emission mainly lies in the P-N junction of the LED chip. Generally speaking, a semiconductor chip is composed of two parts: one is the P-type semiconductor, where holes dominate, and the other is the N-type semiconductor, where electrons dominate. When these two types of semiconductors are connected, a P-N junction is formed.
When current flows through a wire and acts on this chip, electrons are pushed towards the P-region. In the P-region, electrons recombine with holes and release energy in the form of photons. The wavelength of the light, which determines its color, is determined by the material that forms the P-N junction.
LED chips are mainly composed of several elements from arsenic (As), aluminum (Al), gallium (Ga), indium (In), phosphorus (P), nitrogen (N), and silicon (Si), with the main material being monocrystalline silicon.
Classification of LED Chips
Purpose: They are divided into high-power LED chips and low-power LED chips based on their intended use.
Color: They are mainly divided into three types: red, green, and blue (raw materials for producing white light).
Shape: They are generally divided into square and round shapes.
Size: Low-power chips are generally classified as 8mil, 9mil, 12mil, 14mil, etc.
Introduction to LED Chip Structure
Different LED chips have similar structures, consisting of epitaxial chip substrates (such as sapphire substrates, silicon carbide substrates, etc.), doped epitaxial semiconductor materials, and transparent metal electrodes.
Characteristics of LED Chips
- Quaternary chips are prepared using the MOVPE process and are brighter than conventional chips.
- Excellent reliability.
- Wide range of applications.
- High safety.
- Long lifespan.
Important Parameters of LED Chips
- Forward Operating Current (If): It refers to the forward current value when the light-emitting diode operates normally. In practical use, IF should be selected below 0.6·IFm according to needs.
- Forward Operating Voltage (VF): The operating voltage given in the parameter table is obtained at a given forward current, generally measured at IF=20mA. The VF of a light-emitting diode ranges from 1.4 to 3V. VF will decrease as the external temperature rises.
- V-I Characteristics: The relationship between the voltage and current of a light-emitting diode. When the forward voltage is less than a certain value (called the threshold value), the current is extremely small and no light is emitted. When the voltage exceeds a certain value, the forward current increases rapidly with the voltage, causing light emission.
- Luminous Intensity (IV): The luminous intensity of a light-emitting diode usually refers to the luminous intensity in the direction of the normal (for cylindrical light-emitting tubes, it refers to their axis). If the radiation intensity in this direction is (1/683)W/sr, then the light emission is 1 candela (symbolized as cd). Due to the low luminous intensity of general LEDs, luminous intensity is often measured in millicandelas (mcd).
- LED Emission Angle: -90° to +90°
- Spectral Half-Width (Δλ): It indicates the spectral purity of the light-emitting tube.
- Half-Value Angle (θ1/2) and Viewing Angle: θ1/2 refers to the angle between the direction where the luminous intensity value is half of the axial intensity value and the light-emitting axis (normal).
- Full Shape: The angle calculated based on the LED’s luminous solid angle, also known as the plane angle.
- Viewing Angle: It refers to the maximum angle of LED light emission. Different applications have different viewing angles, also known as luminous intensity angles.
- Half Shape: The angle between the normal 0° and the maximum luminous intensity value/2. Strictly speaking, it is the angle corresponding to the maximum luminous intensity value and the maximum luminous intensity value/2. The packaging technology of LEDs results in the maximum luminous angle not being the luminous intensity value at the normal 0°, introducing a deviation angle, which refers to the angle between the maximum luminous intensity corresponding angle and the normal 0°.
- Maximum Forward DC Current (IFm): The maximum forward DC current that can be applied. Exceeding this value can damage the diode.
- Maximum Reverse Voltage (VRm): The maximum reverse voltage that can be applied, also known as the breakdown voltage. Exceeding this value may cause the light-emitting diode to break down and be damaged.
- Operating Environment (topm): The temperature range in which the light-emitting diode can operate normally. Below or above this temperature range, the light-emitting diode will not operate normally, and its efficiency will greatly decrease.
- Allowable Power Consumption (Pm): The maximum value of the product of the forward DC voltage applied across the LED and the current flowing through it. Exceeding this value can cause the LED to overheat and be damaged.