Christopher P. Kocot

High-power truncated-inverted-pyramid (AlxGa1−x)0.5In0.5P/GaP light-emitting diodes exhibiting >50% external quantum efficiency

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).

Backgating in GaAs MESFET's

The phenomenon of backgating in GaAs depletion mode MESFET devices is investigated. The origin of this effect is electron trapping on the Cr2+and EL(2) levels at the semi-insulating substrate-channel region interface. A model describing backgating, based on DLTS and spectral measurements, is presented. Calculations based on this model predict that closely compensated substrate material will minimize backgating. Preliminary experimental data support this prediction.

Anomalies in MODFET's with a low-temperature buffer

GaAs buffer layers grown by molecular-beam epitaxy (MBE) at low temperatures (200-300 degrees C) have been successfully used to reduce sidegating in both MESFETs and MODFETs. There are, however, high concentrations of defects in the low-temperature (LT) buffers that adversely affect the high-frequency performance of precision analog and certain digital circuits. In unoptimized structures, nanosecond and microsecond transients are as large as 85 and 15% of the total voltage swing, respectively. These transients cause various detrimental effects in circuits. These effects are described. Their origin is attributed to the outdiffusion of defects from the LT buffer, and a method for optimizing the device structure for minimum sidegating and maximum high-frequency performance is presented. >

1.4× efficiency improvement in transparent-substrate (AlxGa1−x)0.5In0.5P light-emitting diodes with thin (⩽2000 Å) active regions

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 A and increasing the internal quantum efficiency by using multiple thin (⩽500 A) 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.