Yellow-green emission for ETS-LEDs and lasers based on a strained―InGaP quantum well heterostructure grown on a transparent, compositionally graded AlInGaP buffer

摘要

Epitaxial-transparent-substrate light emitting diodes with a primary emission peak at 590nm and a secondary peak at 560nm have been fabricated in the indium aluminum gallium phosphide (InAlGaP) system. The active layer consists of an undoped, compressively strained indium gallium phosphide (InGaP) quantum well on a transparent In_(0.22)(Al_(0.2)Ga_(0.8))_(0.78)P/ ▽_x[In_x(Al_(0.2)Ga_(0.8))_(1-x)P]/GaP virtual substrate. Theoretical modeling of this structure predicts an accessible wavelength range of approximately 540nm to 590nm (green to amber). Emission with a peak wavelength of 570nm has been observed via cathodoluminescence studies of undoped structures with a quantum well composition of In_(0.35)Ga_(0.65)P. Light emitting diodes have been fabricated utilizing simple top and bottom contacts. The highest LED power of 0.18μW per facet at 20mA was observed for a quantum well composition of In_(0.32)Ga_(0.68)P and a bulk threading dislocation density on the order of 7xl0~6 cm~(-2). The spectrum of this device was composed of two peaks: a weak peak at the predicted 560nm wavelength and a stronger peak at 590nm. Based upon superspots present in electron diffraction from the quantum well region, we believe that the observed spectrum is the result of emission from ordered and disordered domains in the active region. The same device structure grown with a bulk threading dislocation density on the order of 5xl0~7 cm~(-2) exhibited an identical spectral shape with a reduced power of 0.08μW per facet at 20mA. For a quantum well composition of In_(0.37)Ga_(0.63)P and an overall threading dislocation density on the order of 5x10~7 cm~(-2), a single peak wavelength of 588nm with a power of 0.06μW per facet at 20mA was observed.