narrowerbandgap

Narrower bandgap refers to semiconductor materials that have a smaller energy gap between their valence and conduction bands compared with conventional wide-bandgap semiconductors. The bandgap energy, usually denoted Eg, governs the minimum photon energy that can be absorbed and the thermal generation of carriers.

Because Eg is small, narrower bandgap materials can absorb and emit light at longer wavelengths, extending into the near- and mid-infrared. However, the small Eg also increases intrinsic carrier concentration at room temperature, leading to higher dark currents and reduced device voltage in diodes and solar cells. Devices based on narrow bandgap materials often require cooling or special design to mitigate these effects.

Common narrow bandgap materials include mercury cadmium telluride (HgCdTe), indium antimonide (InSb), indium arsenide (InAs), gallium antimonide (GaSb), and lead chalcogenides such as PbS and PbSe. Bandgap can be tuned by alloy composition (for example HgCdTe or InGaAs) or by quantum confinement in wells and nanostructures. Achieving high-quality, lattice-matched materials is technically challenging and sensitive to temperature and impurities.

Applications span infrared imaging and sensing, thermal cameras, spectroscopy, and certain photovoltaic concepts such as near-IR solar cells and thermophotovoltaics. Ongoing research aims to improve material quality, reduce cooling requirements, and integrate narrower-bandgap devices with silicon and other platforms.