A truncated-inverted-pyramid (TIP) chip geometry provides substantial improvement in light extraction efficiency over conventional AlGaInP/GaP chips of the same active junction area (∼0.25 mm2). The TIP geometry decreases the mean photon path-length within the crystal, and thus reduces the effects of internal loss mechanisms. By combining this improved device geometry with high-efficiency multiwell active layers, record-level performance for visible-spectrum light-emitting diodes is achieved. Peak efficiencies exceeding 100 lm/W are demonstrated (100 mA dc, 300 K) for orange-emitting (λp∼610 nm) devices, with a peak luminous flux of 60 lumens (350 mA dc, 300 K). In the red wavelength regime (λp∼650 nm), peak external quantum efficiencies of 55% and 60.9% are measured under direct current and pulsed operation, respectively (100 mA, 300 K).

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We report significant differences between the properties of buried oxides converted from AlGaAs and AlAs layers using selective wet oxidation. Layers of AlxGa1−xAs with x≥0.96 exhibit crystallographic dependent oxidation rates, while for layers with x≤0.92 the oxidation rate is isotropic. Mesas containing partially oxidized layers of AlAs are unstable to rapid thermal cycling and exhibit excessive strain at the oxide terminus, while mesas containing partially oxidized layers of AlGaAs are robust and lack evidence of strain. Finally, the oxidation of AlGaAs layers, rather than AlAs, is found to provide robust oxide apertures for reliable vertical-cavity surface emitting lasers.

Improvement of 1.4× in the external quantum efficiency and luminous efficiency (lm/W) of transparent-substrate (AlxGa1−x)0.5In0.5P/GaP light-emitting diodes is demonstrated. The improvement is accomplished by reducing the thickness of the active layer to ⩽2000 Å and increasing the internal quantum efficiency by using multiple thin (⩽500 Å) active layers. The maximum luminous efficiency achieved is 73.7 lm/W at λp∼615 nm and the maximum external quantum efficiency is 32.0% at λp∼632 nm.

Investigation of short wavelength intersubband transitions in InGaAs/AlAs quantum wells on GaAs substrate