Laser Diodes History
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The History of Laser Diodes: From 1962 to Today
Laser diodes are semiconductor devices that produce coherent light by stimulated emission of photons. They are widely used in various applications, such as fiber optic communications, barcode readers, laser pointers, optical disc drives, laser printing, laser scanning, and light beam illumination. But how did laser diodes come into existence Here is a brief history of their development and evolution.
The First Laser Diode: 1962
The first laser diode was demonstrated in 1962 by two US groups independently. One group was led by Robert N. Hall at the General Electric research center, and the other by Marshall Nathan at the IBM T.J. Watson Research Center. They both used gallium arsenide (GaAs) as the semiconductor material, which emitted infrared light at a wavelength of about 850 nm. The laser diode was a simple p-n junction diode, where electrons and holes recombined in the intrinsic region and generated photons by spontaneous and stimulated emission. The output power was very low, only a few milliwatts, and the efficiency was less than 1%. However, this breakthrough proved that laser action could be achieved in a solid-state device.
The Double-Heterostructure Laser Diode: 1970
The next major advance in laser diode technology came in 1970, when Zhores Alferov from the Soviet Union and Herbert Kroemer from the US independently proposed the concept of a double-heterostructure laser diode. This design improved the confinement of both carriers and photons in the active region, resulting in higher output power, efficiency, and stability. The double-heterostructure laser diode consisted of a thin layer of a direct band-gap semiconductor (such as GaAs) sandwiched between two layers of a wider band-gap semiconductor (such as AlGaAs). The difference in band-gap created an energy barrier that prevented carriers from escaping the active region, and also acted as a waveguide that guided photons along the axis of the device. The first double-heterostructure laser diode was demonstrated by Alferov's group in 1970, using GaAs/AlGaAs as the material system.
The Visible Light Laser Diode: 1976
The first laser diode that emitted visible light was demonstrated in 1976 by Toshio Itoh and Izuo Hayashi from Japan. They used gallium phosphide (GaP) as the semiconductor material, which emitted green light at a wavelength of about 555 nm. The GaP laser diode was also a double-heterostructure device, but with a zinc-diffused p-n junction instead of an epitaxial one. The output power was about 5 mW, and the efficiency was about 0.1%. The visible light laser diode opened up new possibilities for applications such as displays, indicators, and optical storage.
The High-Power Laser Diode: 1980s
In the 1980s, several innovations were made to increase the output power and efficiency of laser diodes. One of them was the quantum well laser diode, which reduced the thickness of the active layer to a few nanometers, creating a quantum confinement effect that enhanced the optical gain and reduced the threshold current. Another one was the distributed feedback (DFB) laser diode, which incorporated a periodic grating structure into the waveguide to provide wavelength-selective feedback and single-mode operation. A third one was the vertical-cavity surface-emitting laser (VCSEL) diode, which used two parallel mirrors to form a resonant cavity perpendicular to the substrate surface, allowing for low-threshold current and high-density integration. These developments enabled laser diodes to achieve output powers of several watts and efficiencies of over 50%, making them suitable for high-power applications such as industrial cutting, welding, and pumping.
The Blue Light Laser Diode: 1996
The last missing piece in the spectrum of laser diodes was blue light, which required a semiconductor material with a band-gap of about 3 eV. The most promising candidate was gallium nitride (GaN), but it was very difficult to grow high-quality crystals and p-type doping. In 1996, Shuji Nakamura from Japan solved these problems by using metal-organic chemical vapor deposition (M aa16f39245