Data are presented demonstrating the operation of transparent-substrate (TS) (AlxGa1−x)0.5In0.5P/GaP light-emitting diodes (LEDs) whose efficiency exceeds that afforded by all other current LED technologies in the green to red (560–630 nm) spectral regime. A maximum luminous efficiency of 41.5 lm/W (93.2 lm/A) is realized at λ∼604 nm (20 mA, direct current). The TS (AlxGa1−x)0.5In0.5P/GaP LEDs are fabricated by selectively removing the absorbing n-type GaAs substrate of a p-n (AlxGa1−x)0.5In0.5P double heterostructure LED and wafer bonding a ‘‘transparent’’ n-GaP substrate in its place. The resulting TS (AlxGa1−x)0.5In0.5P/GaP LED lamps exhibit a twofold improvement in light output compared to absorbing-substrate (AS) (AlxGa1−x)0.5In0.5P/GaAs lamps.
The performance of surface-emitting visible AlGaInP light-emitting diodes (LEDs) is described. The devices have external quantum efficiencies greater than 2% and luminous efficiencies of 20 lm/A in the yellow (590 nm) spectral region. This performance is roughly ten times better than existing yellow LEDs and is comparable to the highest performance red AlGaAs LEDs currently available. The devices also perform favorably compared to existing devices in the orange and green spectral regions. Low-pressure organometallic vapor phase epitaxy (OMVPE) is used to grow the epitaxial layers. The devices consist of a double heterostructure with an AlGaInP active region grown on a GaAs substrate.
The impact ionization coefficients in AlxGa1−xAs have been experimentally determined for compositions x≤0.4. These data are necessary for accurate device design and modeling. Both α, the electron ionization coefficient, and β, the hole ionization coefficient, decrease with increasing x, and there is no appreciable change in the ratio α/β over the range of compositions and electric fields studied.
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