Editing Laser diode (section)

== History ==
[[File:Nick Holonyak Jr.jpg|thumb|[[Nick Holonyak]], inventor of first visible-wavelength semiconductor laser diode]]
Following theoretical treatments of M.G. Bernard, G. Duraffourg, and William P. Dumke in the early 1960s, [[Coherence (physics)|coherent]] light emission from a [[gallium arsenide]] (GaAs) semiconductor diode (a laser diode) was demonstrated in 1962 by two US groups led by [[Robert N. Hall]] at the [[General Electric]] research center<ref>{{cite journal |last=Hall |first=Robert N. |author-link=Robert N. Hall |author2=Fenner, G. E. |author3=Kingsley, J. D. |author4=Soltys, T. J. |author5=Carlson, R. O. |date=November 1962 |title=Coherent Light Emission From GaAs Junctions |journal=Physical Review Letters |volume=9 |issue=9 |pages=366–8 |doi=10.1103/PhysRevLett.9.366 |bibcode=1962PhRvL...9..366H|doi-access=free }}</ref> and by Marshall Nathan at the [[Thomas J. Watson Research Center|IBM T.J. Watson Research Center]].<ref>{{cite journal|last1=Nathan|first1=Marshall I.|last2=Dumke|first2=William P.|last3=Burns|first3=Gerald|last4=Dill|first4=Frederick H.|last5=Lasher|first5=Gordon|title=Stimulated Emission of Radiation from GaAs p–n Junctions|doi=10.1063/1.1777371|year=1962|page=62|volume=1|journal=Applied Physics Letters|url=http://www.ecse.rpi.edu/~schubert/More-reprints/1962%20Nathan%20Dumke%20et%20al%20%28APL%29%20Stimulated%20emission%20of%20radiation%20from%20GaAs%20p-n%20junctions.pdf|archive-url=https://web.archive.org/web/20110503225242/http://www.ecse.rpi.edu/~schubert/More-reprints/1962%20Nathan%20Dumke%20et%20al%20%28APL%29%20Stimulated%20emission%20of%20radiation%20from%20GaAs%20p-n%20junctions.pdf|url-status=dead|archive-date=2011-05-03|bibcode = 1962ApPhL...1...62N|issue=3 }}</ref> There has been ongoing debate as to whether IBM or GE invented the first laser diode, which was largely based on theoretical work by William P. Dumke at IBM's Kitchawan Lab (currently known as the Thomas J. Watson Research Center) in [[Yorktown Heights, New York|Yorktown Heights]], NY. The priority is given to the General Electric group, who submitted their results earlier; they also went further and made a resonant cavity for their diode.<ref>[http://www.aip.org/history/ohilist/4792.html Oral History Transcript — Dr. Marshall Nathan], American Institute of Physics</ref> It was initially speculated, by [[Massachusetts Institute of Technology|MIT]]'s Ben Lax among other leading physicists, that silicon or germanium could be used to create a lasing effect, but theoretical analyses convinced William P. Dumke that these materials would not work. Instead, he suggested gallium arsenide as a good candidate. The first visible-wavelength laser diode was demonstrated by [[Nick Holonyak, Jr.]] later in 1962; he used [[gallium arsenide phosphide]].<ref name="afterglow">{{cite news |title= After Glow |publisher=Illinois Alumni Magazine |date=May–June 2007}}</ref>

Other teams at [[MIT Lincoln Laboratory]], [[Texas Instruments]], and [[RCA Laboratories]] were also involved in, and received credit for, their historic initial demonstrations of efficient light emission and lasing in semiconductor diodes in 1962 and thereafter. GaAs lasers were also produced in early 1963 in the [[Soviet Union]] by the team led by [[Nikolay Basov]].<ref>{{cite web|publisher = Nobelprize.org|url = http://nobelprize.org/nobel_prizes/physics/laureates/1964/basov-bio.html| title = Nicolay G. Basov| access-date = 2009-06-06}}</ref>

In the early 1960s, liquid-phase [[epitaxy]] (LPE) was invented by Herbert Nelson of RCA Laboratories. By layering the highest-quality crystals of varying compositions, it enabled the demonstration of the highest-quality [[heterojunction]] semiconductor laser materials for many years. LPE was adopted by all the leading laboratories worldwide and was used for many years. It was finally supplanted in the 1970s by [[molecular-beam epitaxy]] and organometallic [[chemical vapor deposition]].

Diode lasers of that era operated with threshold current densities of 1000 A/cm<sup>2</sup> at 77 K temperatures. Such performance enabled continuous lasing to be demonstrated in the earliest days. However, when operated at room temperature, about 300 K, threshold current densities were two orders of magnitude greater, or 100,000 A/cm<sup>2</sup>, in the best devices. The dominant challenge for the remainder of the 1960s was to obtain low threshold current density at 300 K and thereby to demonstrate continuous-wave lasing at room temperature from a diode laser.

The first diode lasers were homojunction diodes. That is, the material (and thus the bandgap) of the waveguide core layer and that of the surrounding clad layers were identical. It was recognized that there was an opportunity, particularly afforded by the use of liquid-phase epitaxy using [[Aluminium gallium arsenide|aluminum gallium arsenide]], to introduce heterojunctions. Heterostructures consist of layers of semiconductor crystal having varying bandgap and [[refractive index]]. Heterojunctions (formed from heterostructures) had been recognized by [[Herbert Kroemer]], while working at RCA Laboratories in the mid-1950s, as having unique advantages for several types of electronic and optoelectronic devices, including diode lasers. LPE afforded the technology of making heterojunction diode lasers. In 1963, he proposed the [[double heterostructure]] laser.

The first heterojunction diode lasers were single-heterojunction lasers. These lasers used aluminum gallium arsenide ''p''-type injectors situated over ''n''-type gallium arsenide layers grown on the substrate by LPE. An admixture of aluminum replaced gallium in the semiconductor crystal and raised the bandgap of the ''p''-type injector over that of the ''n''-type layers beneath. It worked; the 300 K threshold currents went down by 10× to 10,000 A/cm<sup>2</sup>. Unfortunately, this was still not in the needed range, and these single-heterostructure diode lasers did not function in continuous-wave operation at room temperature.

The innovation that met the room temperature challenge was the double-heterostructure laser. The trick was to quickly move the wafer in the LPE apparatus between different ''melts'' of aluminum gallium arsenide (''p''- and ''n''-type) and a third melt of gallium arsenide. It had to be done rapidly since the gallium arsenide core region needed to be significantly under 1&nbsp;μm in thickness. The first laser diode to achieve ''[[continuous wave|continuous-wave]]'' operation was a [[double heterostructure]] demonstrated in 1970 essentially simultaneously by [[Zhores Alferov]] and collaborators (including [[Dmitri Z. Garbuzov]]) of the [[Soviet Union]], and [[Morton Panish]] and [[Izuo Hayashi]] working in the United States. However, it is widely accepted that Alferov and team reached the milestone first.<ref name=Chatak>{{cite book|last=Chatak|first=Ajoy|title=Optics|year=2009|publisher=Tata McGraw-Hill Education|isbn=978-0-07-026215-7|pages=1.14}}</ref>

For their accomplishment and that of their co-workers, Alferov and Kroemer shared the [[List of Nobel laureates in Physics|2000 Nobel Prize in Physics]].