Читать книгу VCSEL Industry - Babu Dayal Padullaparthi - Страница 20

The characteristics of the semiconductor diode current (I) as a function of the applied voltage (V) are used to create several different types of optical devices. The voltage–current (V‐I) characteristic of a diode is shown in Figure 1.3. The first quadrant Q1 is known as forward bias, and the current increases exponentially with the applied voltage. When an electron and a hole recombine near the p‐n junction, the energy is released as a photon. This regime is where light‐emitting diodes (LEDs) and lasers operate.

The third quadrant Q3 is the reverse bias region, which is used as photodetectors. When a photon is absorbed near the p‐n junction, the light energy creates an electron and hole pair. The electrons drift to the positive electrode and the holes move to the negative electrode under reverse bias.

The fourth quadrant Q4 is where photoconduction occurs and is the operating regime for solar cells. When a photon is absorbed near the p‐n region, an electron hole pair is created. The resultant current times voltage (power) generates an electrical energy in the solar cell. The second quadrant is not used for practical optical devices.

The first and third quadrants play critical roles as key optoelectronics components for optical communication and sensing applications. To understand how light (photons) interacts with semiconductors, a deeper understanding of light emissions and absorption is needed.

Figure 1.3 Voltage–current (V–I) characteristic of a p‐n junction with no incident light (solid curve) and with incident light (dashed curves).

Source: Figure by K. Iga and J. A. Tatum [copyright reserved by authors].