One of the greatest strengths of semiconductors is their ability to convert between electricity and light. This property is what makes possible devices such as LEDs, lasers, and solar cells — collectively known as photonic semiconductor devices.

 

Emitting light, receiving light, and converting light into electrical power — photonic semiconductor materials are what make all of these phenomena possible.

Photonic semiconductors fall broadly into three categories:

1.Light-emitting devices (LEDs, laser diodes, etc.) → Convert electricity into light (electroluminescence)

2.Light-receiving devices (photodiodes, image sensors) → Convert light into electricity (photoconduction)

3.Solar cells → Convert light energy into electrical power (the photovoltaic effect)

Light-emitting devices rely on direct-gap semiconductors. Because electrons release light as they lose energy, these materials achieve high conversion efficiency.

The main materials used include:

・GaAs (gallium arsenide): Infrared LEDs, laser light sources

・GaP (gallium phosphide): Red and yellow-green LEDs

・GaN (gallium nitride): Blue LEDs, and the foundation of white LEDs

・InGaN and AlGaN: Allow precise wavelength control, covering the full RGB color range

・InP (indium phosphide)>: Infrared lasers for optical communications

In particular, the emergence of GaN-based blue LEDs in the 1990s revolutionized the lighting and display industries. The ability to produce white light gave rise to energy-efficient light sources that could replace fluorescent tubes and incandescent bulbs.

Fiber-optic communication mainly uses the 1.3–1.55μm wavelength band, where signal loss is low, allowing signals to travel long distances.

The main materials used include:

・InP (indium phosphide) based materials: The leading choice for optical communications (a direct-gap material)

・InGaAsP: Used in tunable lasers and photodiodes

・GaAs-based materials: Used for short-wavelength (around 850nm) optical communications and sensors

Compound semiconductors form the very heart of optical communication networks.

Solar cells (solar panels) are devices that convert light energy directly into electrical power. Their main materials have diversified from silicon-based cells to newer thin-film technologies.

1.Silicon-based

・Monocrystalline Si: High efficiency and high reliability (conversion efficiency of roughly 22–25%)

・Polycrystalline Si: Inexpensive and well suited to mass production (efficiency of roughly 18–20%), accounting for roughly 90% of the world’s solar cells

 

2.Compound-based (Group III-V)

・Multi-junction cells built from stacked layers of materials such as GaAs, InGaP, and Ge, achieving conversion efficiency above 30%. Used in space applications and satellites.

 

3.Thin-film based

・CdTe (cadmium telluride)

・CIGS (copper indium gallium selenide)

・Amorphous silicon (a-Si)

These are lightweight, flexible, and low cost, making them suitable for use in buildings and mobile devices as well.

 

4.Next-generation types (still in research and development)

・Perovskite solar cells (low cost, can be manufactured via printing)

・Organic solar cells (flexible and lightweight)

For photonic devices, optical properties matter just as much as electrical properties.

Key factors considered when selecting a material include:

・Band gap size (determines the wavelength of light emitted or absorbed)

・Whether the material is direct-gap or indirect-gap (directly affects emission efficiency)

・Refractive index and transmittance (relevant to optical waveguide design)

・Crystal lattice matching (affects the quality of heterojunctions)

・Thermal conductivity and heat dissipation

For photonic semiconductors, balancing light, heat, and electricity is the key to good design.

Photonic semiconductors — used in solar cells, optical communications, and more — are also a driving technology behind the shift to a decarbonized society.

・LED lighting → Reduces power consumption by roughly 70–80% compared with conventional lighting.

・Solar cells → A means of generating electricity without fossil fuels.

・Optical communications → Improve energy efficiency through fast, low-loss data transmission.

Photonic semiconductors sit at the intersection of environmental technology and IT technology.

・Hybrid perovskite-silicon solar cells are targeting conversion efficiencies above 40%.

・LEDs are advancing toward higher color rendering and brightness through quantum dots and micro-LED technology.

・Optical communications are moving toward even greater speed and lower power consumption through photonic integrated circuits (PICs).

・Infrared photonic semiconductors are becoming central to LiDAR systems used in AI and autonomous driving.

Photonic semiconductors are emerging as a key next-generation technology, bridging the worlds of information and energy.

・Photonic semiconductors sit at the center of technology that converts between light and electricity.

・They enable a wide range of applications, including LEDs, lasers, and solar cells.

・The range of materials in use is expanding from silicon to GaAs, InP, CIGS, and perovskites.

・An era is emerging in which semiconductors handle everything: emitting light, sensing light, and generating electricity.

1.Are light-emitting devices built from direct-gap or indirect-gap materials?

2.What materials are used in solar cells for space applications?

3.Why are perovskite solar cells attracting attention?

 

 

Column Supervisor: Koji Kakumoto (Otis Group Co., Ltd.)

After studying abroad and working in planning and development at a trading company, he joined Otis Group Co., Ltd. in 2011. While primarily working in the Corporate Planning Department, he has also served concurrently in manufacturing and technical divisions, and since 2018 has served as Representative Director, working to drive business growth and strengthen the organization.

 

This article is a general technical explanation intended for educational purposes and does not refer to any specific company, product, or technology.