Broadband light emitting device lamps for providing white light output
View Patent ↗A light emitting device (LED) includes a broadband LED chip having a multi-quantum well active region including alternating active and barrier layers. The active layers respectively include different thicknesses and/or different relative concentrations of at least two elements of a semiconductor compound, and are respectively configured to emit light of different emission wavelengths that define an asymmetric spectral distribution over a wavelength range within a visible spectrum. Related devices are also discussed.
1. A light emitting device (LED), comprising:
a broadband LED chip including a multi-quantum well active region comprising alternating active and barrier layers, the active layers respectively comprising different thicknesses and/or different relative concentrations of at least two elements of a semiconductor compound and respectively configured to emit light of different emission wavelengths that define an asymmetric spectral distribution over a wavelength range within a visible spectrum.
2. The device of claim 1 , wherein the asymmetric spectral distribution of the light emitted by the active layers has a full width at half maximum (FWHM) of greater than about 35 nanometers (nm).
3. The device of claim 1 , wherein the light emitted by the active layers combines to provide an appearance of white light.
4. The device of claim 1 , wherein the wavelength range comprises a broadband blue, green, or red wavelength range.
5. The device of claim 4 , wherein a peak wavelength of the spectral distribution is shifted toward an end of the wavelength range.
6. The device of claim 5 , wherein the peak wavelength is within about 30 nanometers (nm) of the end of the wavelength range.
7. The device of claim 4 , wherein the wavelength range comprises the blue or green wavelength range, and wherein the active layers comprise a first layer of In x Ga 1-x N and a second layer of In y Ga 1-y N, where x and y are not equal.
8. The device of claim 4 , wherein the wavelength range comprises the red wavelength range, and wherein the active layers comprise a first layer of Al x Ga y In 1-x-y P and a second layer of Al w Ga z In 1-w-z P, where x and w are not equal, and where y and z are not equal.
9. The device of claim 1 , further comprising:
an n-type cladding layer on the multi-quantum well active region; and
a p-type cladding layer on the multi-quantum well active region opposite the n-type cladding layer,
wherein respective bandgap energies of the active layers sequentially decrease from the n-type cladding layer to the p-type cladding layer.
10. The device of claim 1 , wherein at least one of the active layers has a non-uniform concentration of the at least two elements over a thickness thereof.
11. The device of claim 1 , wherein at least one of the barrier layers comprises a graded concentration of the at least two elements of the semiconductor compound based on the relative concentrations of the active layers to enhance recombination of carriers therein.
12. The device of claim 1 , wherein the wavelength range over which the active layers are configured to emit light is greater than about 50 nanometers (nm).
13. The device of claim 1 , wherein the wavelength range over which the active layers are configured to emit light is less than about 100 nanometers (nm).
14. The device of claim 1 , wherein an energy associated with the light emitted by one of the active layers is no more than about 125% of an energy associated with the light emitted by another of the active layers within the wavelength range.
15. The device of claim 1 , wherein the device is free of a wavelength conversion material.
16. The device of claim 1 , further comprising:
a second broadband LED chip including a multi-quantum well active region comprising alternating second active and barrier layers, the second active layers respectively comprising different thicknesses and/or different relative concentrations of at least two elements of a second semiconductor compound and respectively configured to emit light of different emission wavelengths that define a second asymmetric spectral distribution over a second wavelength range including wavelengths greater than those of the first wavelength range; and
a third broadband LED chip including a multi-quantum well active region comprising alternating third active and barrier layers, the third active layers respectively comprising different thicknesses and/or different relative concentrations of at least two elements of a third semiconductor compound and respectively configured to emit light of different emission wavelengths that define a third asymmetric spectral distribution over a third wavelength range including wavelengths greater than those of the second wavelength range,
wherein the third semiconductor compound has a narrower bandgap than the second semiconductor compound, wherein the second semiconductor compound has a narrower bandgap than the first semiconductor compound, and wherein the light emitted by the first, second, and third broadband LED chips combines to provide an appearance of white light.
17. The device of claim 16 , wherein a separation between respective center wavelengths of the first and second spectral distributions is not greater than a sum of respective half width at half maximum values of the first and second spectral distributions, and wherein a separation between respective center wavelengths of the second and third spectral distributions is not greater than a sum of respective half width at half maximum values of the second and third spectral distributions.
18. The device of claim 1 , further comprising:
a second broadband LED chip including a multi-quantum well active region comprising alternating second active and barrier layers, the second active layers respectively comprising different thicknesses and/or different relative concentrations of at least two elements of a second semiconductor compound and respectively configured to emit light of different emission wavelengths that define a second asymmetric spectral distribution over a second wavelength range including wavelengths greater than those of the first wavelength range; and
a wavelength conversion material configured to absorb at least some of the light emitted by the first and/or second broadband LED chips and re-emit light of different emission wavelengths over a third wavelength range,
wherein the second semiconductor compound has a narrower bandgap than the first semiconductor compound, and wherein the light emitted by the first and second broadband LED chips and the wavelength conversion material combines to provide an appearance of white light.
19. A light emitting device (LED), comprising:
a broadband LED chip including a multi-quantum well active region comprising alternating active and barrier layers of In x Ga 1-x N where x≧0, the active layers respectively comprising different thicknesses and/or different relative concentrations of indium (In) and gallium (Ga) and respectively configured to emit light of different emission wavelengths corresponding to a same color over either a blue wavelength range or a green wavelength range to define a spectral distribution having a full width at half maximum (FWHM) of greater than about 40 nanometers (nm).
20. The device of claim 19 , wherein the spectral distribution is asymmetric over the blue or green wavelength range.