Double-heterostructure Light-emitting Diodes Research Articles

High-power UV InGaN/AlGaN double-heterostructure LEDs

Ultraviolet (UV) InGaN/AlGaN double-heterostructure (DH) light-emitting diodes (LEDs) with an external quantum efficiency of 7.5%, an output power of 5mW and an emission wavelength of 371nm were developed. High-power UV LEDs are obtained using an InGaN active layer with a thickness of 400Å instead of a GaN active layer. The localized energy states caused by In composition fluctuation in the InGaN active layer are related to the high efficiency of the InGaN-based LEDs.

Characteristics of InGaN/AlGaN light-emitting diodes on sapphire substrates

We report characteristics and degradation of an InGaN/AlGaN double-heterostructure light-emitting diode (LED) grown by metalorganic chemical vapor deposition on a sapphire substrate. The InGaN/AlGaN LED exhibited an optical output power of 0.17 mW, an external quantum efficiency of 0.2%, a peak emission wavelength at 440 nm with a full width at half-maximum of 63 nm, and a stable operation up to 3000 h under 30 mA dc operation at 30 °C. However, the InGaN/AlGaN LED showed electrical and optical degradations under high injected current density and high ambient temperature. Electroluminescence, electron-beam-induced current and cathodoluminescence observations showed that the degraded InGaN/AlGaN LED exhibited formation and propagation of dark regions, which act as nonradiative recombination centers. The values of the degradation rate were determined to be 1.1×10−3, 1.9×10−3, and 3.9×10−3 h−1 under the injected current density of 100 A/cm2, and 1.6×10−2, 3.6×10−2, and 8×10−2 h−1 under 200 A/cm2 at ambient temperatures of 30, 50, and 80 °C, respectively. The activation energy of degradation was also determined to be 0.23–0.25 eV. The degradation of electrical and optical characteristics was caused by the growth of dark regions. It was also observed that GaN-based LEDs on sapphire substrates have longer lifetime than the ZnSe-based LED, but shorter than the AlGaAs and InGaAsP LEDs.

Optical degradation of InGaN/AlGaN light-emitting diode on sapphire substrate grown by metalorganic chemical vapor deposition

We report an optical degradation of an InGaN/AlGaN double-heterostructure light-emitting diode (LED) on a sapphire substrate grown by metalorgonic chemical vapor deposition. Electroluminescence, electron-beam induced current, and cathodoluminescence observations have shown that the degraded InGaN/AlGaN LED exhibits formation and propagation of dark spots and a crescent-shaped dark patch, which act as nonradiative recombination centers. The values of degradation rate under injected current density of 0.1 kA/cm2 were determined to be 1.1×10−3, 1.9×10−3, and 3.9×10−3h−1 at ambient temperatures of 30, 50, and 80°C, respectively. The activation energy of degradation was also determined to be 0.23 eV.

Degradation of InGaN/AlGaN LED on Sapphire Substrate Grown by MOCVD

ABSTRACTWe report an optical degradation of an InGaN/AIGaN double-heterostructure light-emitting diode (LED) on a sapphire substrate grown by metalorganic chemical vapor deposition. The InGaN/AIGaN LED exhibited an optical output power of 0.17 mW, external quantum efficiency of 0.2 %, and the peak emitting spectrum at 437 nm with full width at half-maximum of 63 nm under 30 mA dc operation at 300 K. The InGaN/AIGaN LED showed the optical degradation under high injected current density. Electroluminescence, electron-beam induced current and cathodoluminescence observations show that the degraded InGaN/AIGaN LED exhibits formation and propagation of dark spots and a crescent-shaped dark patch, which act as nonradiative recombination centers. The values of degradation rate under injected current density of 0.1 kA/cm2 were determined to be 1.1 × 10-3, 1.9 × 10-3 and 3.9 × 10-3 h-1 at ambient temperatures of 30, 50 and 80°C, respectively. The activation energy of degradation was also determined to be 0.23 eV.

Light emitting diode-based nanosecond ultraviolet light source for fluorescence lifetime measurements

A compact pulsed-light source is devised from an InGaN/AlGaN double heterostructure light-emitting diode (LED). The LED emits a 450-nm (blue) light under conventional dc operation below 30 mA. When a current larger than 50 mA is applied, the intensity of the 450-nm light saturates, but that of the 380-nm light due to the InGaN component continues to increase. This phenomenon is utilized to realize a nanosecond ultraviolet (UV) light source. Under repetitive, large current pulsing (frequency=10 kHz, pulse width=4 ns, peak current=2 A), the peak LED emission shifts from 450 to 380 nm. Intense light pulses (peak value=40 mW) of 4-ns duration were generated. To evaluate the potential of the pulsed LED as an excitation source, the fluorescence lifetime of a quinine-sulfate solution was measured. The observed lifetime characteristics agreed well with the generally accepted behavior.

First Fabrication of AlGaAs/GaAs Double-Heterostructure Light-Emitting Diodes Grown on GaAs(111)A Substrates Using Only Silicon Dopant

We have grown an AlGaAs/GaAs double-heterostructure (DH) light-emitting diode (LED) on a GaAs(111)A-5°-misoriented substrate using only Si dopant by molecular beam epitaxy. Conduction type and carrier concentration were controlled by flux ratio and Si cell temperature. Smooth heterointerfaces were also obtained. The p-n junction showed a turn-on voltage of 1.2 V and a reverse voltage of 2.5 V at 1 mA. The AlGaAs/GaAs LED exhibited dc operation at 300 K. The optical output power was 30 nW at 150 mA, and the peak in the spectrum was 875 nm with the full width at half-maximum of 28 nm.

AlGaInP orange light-emitting diodes grown on misoriented p-GaAs substrates

AlGaInP double-heterostructure light-emitting diodes (LEDs) grown on misoriented p-GaAs substrates cut 15°-off the (100) plane toward the [011] direction have been fabricated. The device performance was found to be strongly dependent on the doping levels in both cladding layers. The light output first increases up to 39 mcd and then decreases with further increases in the Si-doping level. However, for the lower cladding layer with high doping levels, the decay of light output is caused by an increase of nonradiative recombination due to the Zn diffusion into the active layer. When prepared by the optimum doping concentrations, the external quantum efficiency at 20 mA is 0.6%, corresponding to a luminous intensity of 39 mcd at 615 nm orange light for the AlGaInP bare chips.

Liquid-phase epitaxial growth and characterization of InGaAsP layers grown on GaAsP substrates for application to orange light-emitting diodes

The growth conditions of undoped InGaAsP layers grown on GaAs0.61P0.39 substrates and effects of Te and Zn-doping on electrical and optical properties have been examined in detail. The narrowest full widths at half-maximum (FWHM) of photoluminescence (PL) spectra were measured to be 40 meV at 300 K and 12 meV at 8 K for an undoped InGaAsP sample with a background electron concentration of 2×1016 cm−3. Room-temperature carrier concentrations in the range of 1.8×1017–3.4×1018 cm−3 for n-type dopant and 1.6×1017–2.8×1018 cm−3 for p-type dopant are obtained reproducibly. The 50 K PL spectra of Zn-doped layers show three distinctive peaks and their relative intensities change with various hole concentrations. Visible light-emitting diodes (LEDs) emitting at 619 nm and employing the InGaP/InGaAsP/InGaP double-heterostructure (DH) grown on a lattice-matched GaAs0.61P0.39 substrate have been fabricated. The DH LEDs are characterized by current-voltage (I-V) measurement, electroluminescence (EL), light output power, and external quantum efficiency. A forward-bias turn-on voltage of 1.8 V with an ideality factor of 1.3 and a breakdown voltage of 16 V are obtained from the I-V measurements. The emission peak wavelength and FWHM of room-temperature EL spectra are around 619 nm and 48 meV (15 nm) at 20 mA, respectively. The light output power of the bare diodes is as high as 0.32 mW at a dc current of 100 mA and an external quantum efficiency of 0.22% is observed.

Numerical model of a proposed double heterostructure light-emitting diode for mid-infrared applications

A numerical model of a proposed InAs/InAs0.88Sb0.12 double heterostructure lightemitting diode (DH-LED) has been developed for its d.c. and transient characterization in the 3 to 5 μm wavelength region. The dependence of the optical power and bandwidth on interfacial recombination and self-absorption have been studied. The active layer width has been optimized against interfacial recombination and self-absorption for maximum optical power, bandwidth and power-bandwidth products. The dependence of the power-bandwidth product of the DH-LED on the drive current for different active layer doping concentrations has also been studied. The electrical confinement in the proposed heterostructure has been estimated and its variation with the active layer thickness has been studied. The rise time of the proposed LED has been calculated by using the results of the transient analysis. On the basis of the proposed model, the device is expected to find useful applications as an optical source in future generations of fibre-optic communication systems in the 3 to 5 μm wavelength region.

Very high-efficiency semiconductor wafer-bonded transparent-substrate (AlxGa1−x)0.5In0.5P/GaP light-emitting diodes

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.

AlGaInP/GaInP double-heterostructure orange light-emitting diodes on GaAsP substrates prepared by metalorganic vapor-phase epitaxy

Al 0.33Ga 0.32In 0.35P/Ga 0.65In 0.35P double-heterostructure (DH) light-emitting diodes (LEDs) grown on GaAs 0.7P 0.3 substrates have been fabricated by low-pressure metalorganic vapor-phase epitaxy. We investigate the band gap energy as a function of Al composition in the undoped Al x Ga 0.65− x In 0.35P alloy with x = 0.0−0.195. Effects of Si and Zn doping on electrical properties have been examined by using disilane and dimethylzinc sources. The DH LED on a bare chip exhibits an emission wavelength around 615 nm and an external quantum efficiency of 0.156% at 20 mA.

High-power InGaN/GaN double-heterostructure violet light emitting diodes

InGaN/GaN double-heterostructure light-emitting diodes were fabricated. The output power was 90 μW and the external quantum efficiency was as high as 0.15% at a forward current of 20 mA at room temperature. The peak wavelengths of the electroluminescence (EL) varied between 411 and 420 nm with changes in the growth temperatures of an InGaN active layer between 820 and 800 °C. The full widths at half maximum of EL were between 22 and 25 nm.

Double-heterostructure Ga0.68In0.32P/Ga0.88In0.12As0.34P0.68//Ga0.68In0.32P orange light-emitting diodes

Visible light-emitting diodes (LEDs) emitting at 6l9nm and employing the InGaP/InGaAsP double heterostructure (DH) grown on a lattice-matched GaAs0.61P0.39 substrate have been fabricated for the first time. The orange DH LEDs exhibit an external quantum efficiency of 0.22% and a full width at half maximum of 48meV (15nm) in the electroluminescence spectra.

(Al0.5Ga0.5)0.65In0.35P/Ga0.65In0.35P double-heterostructure orange light-emitting diodes

Visible light-emitting diodes (LEDs) emitting at 615 run and employing the AlGalnP/GalnP double heterostructure (DH) grown on a lattice-matched GaAso.7P0.3 substrate have been fabricated for the first time. The external quantum efficiency of 0.156% for the orange LEDs can be achieved by introducing the GaP material as the current spreader and window layer for the DH LEDs.

Comparison of single- and double-heterostructure AlGaAs/InGaP red light-emitting diodes prepared by liquid-phase epitaxy

The performance of the AlGaAs/InGaP single-heterostructure (SH) and AlGaAs/InGaP/AlGaAs double-heterostructure (DH) light-emitting diodes (LEDs) is compared. For these two types of LEDs, they have a very shining surface morphology and flat interface. However, the SH LEDs always exhibit better properties than the DH LEDs in the ideality factor, electroluminescence, light output power, and external quantum efficiency. From the x-ray diffraction measurements, we find that the main problem for the undesirable performance of DH LEDs is attributed to the difficulty of obtaining the high quality InGaP/AlGaAs heterostructure. Furthermore, by the Auger-depth-profile measurements, it is found that the P atoms with a very high diffusivity will diffuse into the as-grown AlGaAs layer during the growth of InGaP and thus destroy the heterostructure quality.

Doping concentration dependence of radiance and optical modulation bandwidth in carbon-doped Ga0.51In0.49P/GaAs light-emitting diodes grown by gas source molecular beam epitaxy

Double-heterostructure light-emitting diodes (LEDs) consisting of an n-Ga0.51In0.49P emitter, a carbon-doped p-GaAs active layer, and a p-Al0.30Ga0.70As cladding layer have been grown by gas source molecular beam epitaxy with halomethane carbon doping sources. CCl4 and CHCl3 have been used to vary the active layer C doping level from 1018 to 1020 cm−3. Measurements of LED optical modulation bandwidth indicate that the bandwidth increases with C doping, attaining a record value of 1.6 GHz at 1020 cm−3 C concentration. The LED radiance is observed to decline significantly in the 1019–1020 cm−3 range.

Through-wafer optical communication using monolithic InGaAs-on-Si LEDs and monolithic PtSi-Si Schottky-barrier detectors

Through-wafer optical communication has been demonstrated in experiments employing two vertically stacked Si wafers, the upper one with In/sub 0.15/Ga/sub 0.85/As-In/sub 0.15/Al/sub 0.85/As double-heterostructure LEDs (light-emitting diodes) grown by molecular beam epitaxy on its top surface and the lower one with PtSi-Si Schottky-barrier detectors fabricated on its bottom surface. Infrared radiation emitted by the LEDs in a band peaking at 1.12 mu m, just beyond the Si absorption edge, is transmitted through the upper Si wafer, focused with a 25-mm focal-length lens, transmitted through the lower Si wafer, and detected by the Pt-Si detectors. For a single LED-detector pair, the detector signal-to-noise ratio was 10:1 for an LED drive current, of 1 mA at room temperature. The results suggest that through-wafer communication using LEDs and Schottky-barrier detectors is a promising approach for optical interconnects in stacked wafer architectures. >

High-frequency operation of heavily carbon-doped Ga0.51In0.49P/GaAs surface-emitting light-emitting diodes grown by metalorganic molecular beam epitaxy

Single-heterostructure light-emitting diodes (LEDs) consisting of a wide band-gap N-Ga0.51In0.49P emitter and a heavily carbon-doped p-GaAs active layer have been grown by metalorganic molecular beam epitaxy. Trimethygallium has been utilized to dope the GaAs active layer for a hole concentration of 1.5×1020 cm−3 in order to reduce the radiative lifetime of minority carriers in GaAs. The cw electroluminescent spectra of these LEDs indicate that the injection efficiency of the Ga0.51In0.49P/GaAs heterojunction is not degraded by carbon redistribution, even in the absence of an undoped spacer layer between the GaAs active layer and the Ga0.51In0.49P emitter layer. The transient optical response of the LEDs determines an optical 3 dB bandwidth in the range of 0.6–2.0 GHz. The external brightness of the carbon-doped LEDs is shown to be approximately a factor of 20 lower than that of double-heterostructure LEDs containing active layers more moderately doped with Be at 2×1018 cm−3.

High-efficiency InGaAlP/GaAs visible light-emitting diodes

High-efficiency InGaAlP surface emission light emitting diodes (LEDs) have been successfully fabricated. Newly designed double-heterostructure LEDs with a GaAlAs current spreading layer were employed to expand the light emission area, which is necessary to take out the light efficiently. The external quantum efficiency was 1.5% at 620 nm orange light for an In0.5 (Ga0.8Al0.2)0.5P active layer LED. This LED is five times more efficient at 620 nm than that of the GaAlAs and GaAsP LEDs. 563 nm green electroluminescence, which is the shortest wavelength ever reported for InGaAlP LEDs, was also achieved with an In0.5(Ga0.5Al0.5)0.5P active layer.

Al0.3Ga0.7As/Al0.05Ga0.95As light-emitting diodes on GaAs-coated Si substrates grown by liquid phase epitaxy

Al0.3Ga0.7As/Al0.05Ga0.95As double-heterostructure light-emitting diodes (LED’s) were successfully grown for the first time by liquid phase epitaxy on a GaAs-coated Si substrate that was prepared by a sequential process of migration-enhanced epitaxy and molecular beam epitaxy. The edge-emitting LED’s had diode ideality factors of 1.54 at a forward-biased voltage higher than 0.9 V and external quantum efficiencies of 3.3×10−3 W/A per facet. This efficiency is 50 times higher than the previously reported value, and is on the same order as that of AlGaAs homojunction LED’s fabricated on the GaAs substrates by liquid phase epitaxy.