LED Reverse Voltage Breakdown

One method for fabricating a light-emitting diode (LED) involves the deposition of three distinct semiconductor layers onto a substrate. The central, "active region" lies sandwiched between a p-type and an n-type semiconductor layer. Within this active region, light emission occurs when an electron and its corresponding hole recombine. Analyzing the p-n junction as a diode, forward bias drives holes from the p-type material and electrons from the n-type material into the active region. This electron-hole recombination facilitates light generation through a solid-state process known as electroluminescence.

The specific design described facilitates omnidirectional emission of light from the layered structure. To optimize light output, the LED structure is encased within a diminutive, reflective cup. This cup serves to reflect light produced by the active region towards the intended exit direction.

In a standard p-n junction diode, reverse voltage breakdown happens relatively straightforwardly. When a sufficiently large reverse voltage is applied, the electric field across the depletion region becomes powerful enough to rip electrons from their covalent bonds, creating electron-hole pairs through impact ionization. This avalanche multiplication rapidly increases the reverse current, leading to breakdown.

However, LEDs differ from standard diodes in their structure, introducing complexities to reverse voltage breakdown:

1. Multiple Layers and Material Properties: LEDs, especially advanced ones, often have more than just two layers. Each layer can have different bandgaps, doping levels, and carrier mobilities, impacting the electric field distribution and breakdown mechanisms. In some regions, tunneling processes might dominate breakdown instead of impact ionization.

2. Carrier Injection and Confinement: Unlike standard diodes, LEDs are designed to inject carriers into the active region for light emission. Under reverse bias, this injection continues, injecting holes and electrons into opposite sides of the active region. These injected carriers can contribute to additional breakdown mechanisms like band-to-band tunneling and trap-assisted tunneling.

3. Localized Breakdown Risks: Due to the complex layer structure and carrier injection, breakdown doesn't necessarily occur uniformly across the whole device. Localized high electric fields near interfaces or within specific layers can lead to premature breakdown at lower voltages compared to a single-junction diode.

4. Degradation due to Breakdown: Reverse voltage breakdown in LEDs can cause significant damage. High carrier currents and localized heating can degrade the active region, leading to increased leakage currents and eventually permanent performance loss.

Therefore, the multiple layers of an LED introduce various complexities to reverse voltage breakdown, including different breakdown mechanisms, carrier injection effects, localized breakdown risks, and potential for device degradation.