Silicon electroluminescent device

Details Silicon electroluminescent device Silicon electroluminescent device

1989-11-06

1991-12-31

Seidleck, James J.

Stock material or miscellaneous articles

Composite

Of inorganic material

313506, 357 61, 357 63, 357 17, 437 15, 437 20, 437 17, 437173, 437905, 428917, B32B 900, H05B 3314, H05B 3322

Patent

active

050771434

DESCRIPTION:

BRIEF SUMMARY
BACKGROUND OF THE INVENTION

1. Field of the Invention
This invention relates to a silicon electroluminescent device.
2. Discussion of Prior Art
Silicon electroluminescent devices are required for the emerging field of integrated circuits incorporating integrated optical, electronic and electro-optical components. In IEEE Journal of Quantum Electronics, Vol QE-22, No 6, June 1986, Soref and Lorenzo describe silicon waveguides and electro-optical switches suitable for incorporation in conventional silicon integrated circuits. Silicon waveguides in particular are suitable for transmission of the fibre-optic communications wavelength interval 1.3-1.55 .mu.m. The field of silicon integrated optics does however lack one important component; an electroluminescent light source in the 1.3-1.55 .mu.m wavelength interval suitable for integration in silicon.
Electroluminescence relates to the production of light (luminescence) by a medium in response to passage of an electric current through the medium. A GaAs semiconductor light emitting diode (LED) is a common form of electroluminescent device. Such a diode has a pn junction which is forward biased in operation. Minority carriers are injected by the junction into regions of the diode where recombination takes place giving rise to luminescence. This process is not the only recombination route, and its efficiency may be expressed in terms of the number of photons produced per injected carrier (normally much less than unity). Moreover, photons may be reabsorbed in the device after they are produced. Accordingly, the process may be characterised by internal and external quantum efficiencies. Of these the former is the number of photons produced per injected carrier and the latter the number externally detected per injected carrier. The latter is necessarily of lower magnitude. It can be very much lower, since diode electrode and junction geometry requirements tend to conflict with those of photon output. In the related field of photoluminescence, in which a light beam is used to create free carriers for recombination, similar quantum efficiencies are defined. However, their values tend to differ less because no junction or electrode structure is required.
Group III-V LEDs such GaAs or InGaAsP devices are highly efficient and well developed; they exhibit internal quantum efficiencies of between 0.2 and 0.05. However, not being silicon-based, they cannot be easily integrated in silicon.
Silicon-based electroluminescent devices have been described in the prior art which produce luminescence from the following processes: silicon.
Electroluminescence arising from band to band transitions in pn junction silicon diodes is described by Haynes et al, Phys Rev 101, pp 1676-8 (1956), and by Michaels et al, Phys Stat Sol 36, p311 (1969). However, the internal quantum efficiency is in the region of 10.sup.-5, four orders of magnitude lower than conventional LEDs. It is a consequence of the indirect nature of the bandgap in silicon, which is a fundamental problem.
A silicon LED incorporating a rare earth dopant is disclosed by Ennen et al, Appl Phys Lett 46(4), 15 Feb. 1985, pp 381-3. This device consisted of epitaxially grown n and p type silicon layers doped with erbium. The Er dopant was introduced by implantation providing an ion concentration of 5.6.times.10.sup.18 cm.sup.-3. The diode exhibited an external quantum efficiency of 5.times.10.sup.-4, which the authors observed was not of the order acceptable for device applications. It is about two orders of magnitude below that of conventional LEDs. Furthermore, rare earth ion implantation is disadvantageous for integrated circuit applications, since it is not electrically inactive; i.e. it introduces unwanted energy levels into the semiconductor forbidden gap. These levels tend to disrupt the electrical properties of the host silicon. In this connection, the Ennen et al device exhibits poor rectifying characteristics. Carrier injection, quantum efficiency and luminescence are therefore poor. Rare earth dopants are also unlikely

REFERENCES:
patent: 4071945 (1978-02-01), Karatsjuka et al.
patent: 4857803 (1989-08-01), Anderson, Sr.

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