Group III nitride LED with undoped cladding layer and multiple quantum well

#The present invention relates to semiconductor structures of light emitting devices, particularly light emitting diodes and laser diodes formed from Group III nitrides, which are capable of emitting light in the red to ultraviolet portions of the electromagnetic spectrum.

#Photonic semiconductor devices fall into three categories: devices that convert electrical energy into optical radiation (e.g., light emitting diodes and laser diodes); devices that detect optical signals (e.g., photodetectors); and devices that convert optical radiation into electrical energy (e.g., photovoltaic devices and solar cells). Although all three kinds of devices have useful applications, the light emitting diode may be the most commonly recognized because of its application to various consumer products and applications.

#Light emitting devices (e.g., light emitting diodes and laser diodes), herein referred to as LEDs, are photonic, p-n junction semiconductor devices that convert electrical power into emitted light. Perhaps most commonly, LEDs form the light source in the visible portion of the electromagnetic spectrum for various signals, indicators, gauges, and displays used in many consumer products (e.g., audio systems, automobiles, household electronics, and computer systems). LEDs are desirable as light output devices because of their generally long lifetime, their low power requirements, and their high reliability.

#FIG. 1 is a cross-sectional schematic view of the aspects of a semiconductor structure for a light emitting device according to the present invention;

#FIG. 2 is a plot of bandgap energy versus lattice parameter for Group III nitrides alloys of aluminum, indium, and gallium (assuming a linear interpolation);

#FIG. 3 is a cross-sectional schematic view of an embodiment of the semiconductor structure;

#The present invention is a semiconductor structure for light emitting devices that can emit in the red to ultraviolet portion of the electromagnetic spectrum. In a first embodiment, the structure includes a Group III nitride active portion positioned between a first n-type Group III nitride cladding layer and a second n-type Group III nitride cladding layer. The active portion preferably includes an active layer and a quantum well or a multiple quantum well as described further later herein. The second n-type cladding layer is characterized by the substantial absence of magnesium (i.e., magnesium may be present, but only in amounts that are so small as to have no functional effect on the semiconductor device). The semiconductor structure itself is further characterized by a p-type Group III nitride layer, which is positioned in the semiconductor structure such that the second n-type cladding layer is between the p-type layer and the active layer. In addition, the active layer has a bandgap that is smaller than each respective bandgap of the first and second n-type cladding layers. As used herein, the term “layer” generally refers to a single crystal epitaxial layer.

#A particular conductivity type (i.e., n-type or p-type) may be unintentional, but is more commonly a result of specifically doping the Group III nitrides using the appropriate donor or acceptor atoms. It is desirable to include layers of opposite conductivity types in order to form a p-n junction in the device. Under forward voltage bias, minority carriers injected across the p-n junction recombine to produce the desired luminescent emissions. Appropriate doping of Group III nitrides is well understood in the art and will not be further discussed herein other than as necessary to describe the invention.

#In general, the active portion and the cladding layers comprise Group III-nitride compounds. The Group III elements in such compounds may be aluminum, indium, gallium, or a combination of two or more such elements.