Electric lamp and discharge devices – With luminescent solid or liquid material – Solid-state type
Reexamination Certificate
1998-07-14
2001-07-24
Patel, Ashok (Department: 2879)
Electric lamp and discharge devices
With luminescent solid or liquid material
Solid-state type
C313S499000, C313S503000, C257S010000, C257S021000, C257S022000
Reexamination Certificate
active
06265823
ABSTRACT:
The present invention relates to a light emitter and in particular to a light emitter that relies upon quantum particle luminescence.
Light emitters based upon the injection of electrons and holes into a nanocomposite material in which small semiconductor particles (quantum particles) are embedded in a glass or polymer matrix have been developed commonly using porous silicon as the material of the semiconductor particles. Ideally, one of the electrodes is at least semi-transparent to allow the light generated by electron-hole recombination in the semiconductor particles to escape the device. To date the material in widespread use for forming the semi-transparent contact is indium tin oxide (ITO). ITO, though, along with all of the other semi-transparent contact materials currently considered, is a degenerate n-type semiconductor with a large electron affinity. The line-up of the energy levels between the n-type ITO and SiO
2
/Si particle system is such that hole injection from the ITO will be extremely unlikely and very inefficient (10
−5
-10
−6
%). Moreover, existing light emitters encounter an additional problem in fabricating a reliable contact to the porous silicon because the porous silicon is such a fragile material.
Reference has been made above to semiconductor quantum particles. It is to be understood that in the context of this document reference to semiconductor quantum particles is intended as reference to semiconductor material in shapes having thicknesses in one or more dimensions approximately of the order of 1-50 nm.
The present invention seeks to provide a quantum particle light emitter having a greater efficiency than that of known quantum particle light emitters. The present invention also preferably seeks to overcome at least some of the disadvantages of known light emitters described above.
The present invention provides a light emitter comprising a substrate having an upper quantum particle layer containing semiconductor quantum particles that are electroluminsescent on application of a biasing voltage; and first and second contacts with at least one of said contacts being at least partially transparent further characterised by a hole transporter provided between the upper quantum particle layer of the semiconductor material and said first contact wherein the hole transporter at least partially intermixes with the upper quantum particle layer.
With the present invention, the efficiency of the light emitter can be increased by around two orders of magnitude in comparison to conventional devices.
Preferably an n-type semiconductor material is used for the substrate and the upper quantum particle layer, for example silicon. More preferably, the upper quantum particle layer is made from porous silicon. A p-type semiconductor material may be used for the first contact, for example NiO. The hole transporter may be polyvinylcarbazole.
In a further aspect the present invention provides a method of fabricating a light emitter comprising: providing a quantum particle layer and a layer of a hole transporting material; applying one layer to the other to cause intermixing at the interface thereof; forming a first contact to the layer of hole transporting material and forming a second contact on the substrate.
In a preferred embodiment an upper layer of an n-type semiconductor material is anodised to form a porous upper quantum particle layer and the hole transporting layer is then applied so as to at least partially penetrate the porous upper quantum particle layer.
In an alternative preferred embodiment a polymer hole transporting layer is applied over the upper surface of the first contact and then a polymer material containing a suspension of quantum particles is spun coated over the top of the hole transporting layer whereby intermixing of the two layers at the interface occurs.
REFERENCES:
patent: 4486499 (1984-12-01), Morimoto
patent: 4801994 (1989-01-01), Van Gorkom et al.
The fabrication and characterization of nickel oxide films and their application as contacts to polymer/porous silicon electroluminescent devices; G Wakefield, P.J. Dobson, Y Y Foo, A Simons and J.I. Hutchison; Semic. Sci. Technol. Dec. 1997 1304-1309, Printed in U.K.
Dobson Peter James
Wakefield Gareth
Isis Innovation Limited
Nixon & Vanderhye P.C.
Patel Ashok
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