Designs for increased efficiency visible wavelength light emitting diodes

This work demonstrates the effectiveness of an {dollar}rm Insb2Osb3{dollar} current spreading layer and underlying {dollar}rm Alsb{lcub}0.6{rcub}Gasb{lcub}0.4{rcub}{dollar}As/AlAs distributed Bragg reflector (DBR) in improving the electrical-to-optical power conversion efficiency of p-n junction visible wavelength light emitting diodes (LEDs). These two design modifications yield a 15-fold improvement in the performance of a red AlGaAs-based structure prepared and tested as a control. The {dollar}rm Insb2Osb3{dollar} current spreading layer increases the power conversion efficiencies of orange, amber, and yellow AlGaInP LEDs. The electrical properties of interfaces between {dollar}rm Insb2Osb3{dollar} and p-type semiconductors are also investigated. A widely used expression for the functional dependence of current on voltage at reverse-biased tunnel junctions is found to be quite accurate in predicting the electrical conductivity of interfaces between {dollar}rm Insb2Osb3{dollar} and arbitrary p-type semiconductors. The optical and electrical properties of {dollar}rm Alsb{lcub}0.6{rcub}Gasb{lcub}0.4{rcub}{dollar}As/AlAs DBRs are studied and exploited. These two indirect band gap semiconductors can be used in epitaxial structures which provide greater than 75% peak reflectivity for all colors in the visible spectrum. Peak reflectivities approaching 100% are demonstrated for visible photons with energies larger than the indirect band gap of {dollar}rm Alsb{lcub}0.6{rcub}Gasb{lcub}0.4{rcub}{dollar}As. These two AlGaAs alloys were also specifically chosen to tailor a conduction band profile which reduces the series resistance due to the heterointerfaces in these n-type structures. A procedure to calculate the resistance of both n and p-type DBRs is developed and used to show that the dominant component of the series resistance in our structures is the resistivity of the material.