M. R. Krames

A dual-wavelength indium gallium nitride quantum well light emitting diode

We have designed and implemented a monolithic, dual-wavelength blue/green light emitting diode (LED) consisting of two active indium gallium nitride/gallium nitride (InGaN/GaN) multiple-quantum-well segments. The segments are part of a single vertical epitaxial structure in which a p++/n++ InGaN/GaN tunnel junction is inserted between the LEDs, emitting in this proof-of-concept device at 470 nm and 535 nm, respectively. The device has been operated as a three-terminal device with independent electrical control of each LEDs to a nanosecond time scale.

Vertical cavity violet light emitting diode incorporating an aluminum gallium nitride distributed Bragg mirror and a tunnel junction

We have designed and implemented a vertical cavity violet light emitting diode which features an optical resonator composed of an in situ grown GaN/AlGaN DBR and a high reflectivity dielectric mirror. The active InGaN MQW medium is grown directly atop the AlGaN DBR and the structure includes an intracavity lateral current spreading layer based on a p++/n++ InGaN/GaN tunnel junction. Electroluminescence shows directional emission, with modal linewidths as narrow as 0.6 nm.

A vertical cavity light emitting InGaN quantum well heterostructure

A method is described for fabricating a vertical cavity light emitting structure for nitride semiconductors. The process involves the separation of a InGaN/GaN/AlGaN quantum well heterostructure from its sapphire substrate an its enclosure by a pair of high reflectivity, low loss dielectric mirrors to define the optical resonator. We have demonstrated a cavity Q factor exceeding 600 in initial experiments, suggesting that the approach can be useful for blue and near ultraviolet resonant cavity light emitting diodes and vertical cavity lasers.

A vertical injection blue light emitting diode in substrate separated InGaN heterostructures

A vertical injection, light emitting InGaN quantum well diode has been demonstrated by separating the nitride heterostructure from its sapphire substrate by ultraviolet laser photoablation within a process scheme that allows transferring the devices to a host substrate. The incorporation of a dielectric multilayer stack to the device is shown to be a first practical step towards a resonant cavity light emitting diode.

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.

Planar single‐facet teardrop‐shaped AlxGa1−xAs‐GaAs quantum well heterostructure laser

Data are presented demonstrating the laser operation of an AlxGa1−xAs‐GaAs quantum well heterostructure (QWH) crystal patterned into a smoothly curved folded resonator, a ‘‘teardrop’’‐shaped resonator, with a single output facet. A deep AlxGa1−xAs native oxide formed entirely through the top confining layer is utilized to produce a large effective index step for lateral optical confinement. The teardrop‐shaped laser operates primarily in a TM (transverse magnetic) longitudinal mode polarized with a TM/TE (transverse electric) power ratio of 7:1. Continuous wave 300 K threshold currents as low as ∼127 mA, external differential quantum efficiencies of η∼15%, and total output power in excess of 75 mW (uncoated facet) are achieved.

A high injection resonant cavity violet light emitting diode incorporating (Al, Ga)N distributed bragg reflector

A vertical cavity violet LED has been designed and implemented which includes an optical resonator composed of an in-situ grown GaN/AlGaN DBR and a high reflectivity dielectric mirror. The structure incorporates an intracavity lateral current spreading layer based on a p ++ /n ++ InGaN/GaN tunnel junction. Electroluminescence shows directional emission, with modal line-widths as narrow as 0.6 nm.

Chapter 2 High-Efficiency AlGalnP Light-Emitting Diodes

Publisher Summary This chapter focuses on the development and performance of aluminum gallium indium phosphide (AlGaInP) light-emitting diodes (LEDs). The AlGaInP quaternary alloy system is widely used for visible wavelength optical devices such as lasers and light-emitting diodes (LEDs). AlGaAs direct bandgap red LEDs, first as absorbing substrate (AS) devices and later as transparent substrate (TS) devices, grown by liquid phase epitaxy (LPE) resulted in improved efficiencies of ∼10 lm/W (∼14% radiant efficiency). These were the first LED devices to take advantage of the efficient double heterostructure (DH) design and made outdoor applications such as red traffic-signal lights and automobile brake lighting a possibility. AlGaInP is an important optoelectronic material for LED and visible laser diode applications. Recent advances in GaN technology have provided efficient blue and green emitters, which make full color displays possible.

Improved thermal stability of AlGaAs–GaAs quantum well heterostructures using a ‘‘blocking’’ Zn diffusion to reduce column‐III vacancies

Data are presented on the reduction of layer intermixing (disordering) in AlGaAs–GaAs quantum well heterostructures (QWH) during high‐temperature anneals by an initial low‐temperature ‘‘blocking’’ Zn diffusion. Room‐temperature photoluminescence measurements of the increase in the lowest electron‐to‐heavy‐hole transition energy in the QW are used to characterize the extent of layer intermixing. Doped (C and Si) samples annealed (850 °C, 12 h) after a low‐temperature blocking Zn diffusion (480 °C) exhibit reductions in energy shift from ∼177 meV to as little as ∼18 meV. Similar effects are also observed, but to a lesser extent, for undoped samples. The improved thermal stability is attributed to a Zn‐diffusion induced reduction in the number of column‐III vacancies in the active layers and is confirmed by secondary‐ion mass spectroscopy measurements.