R. M. Fletcher

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.

HIGH PERFORMANCE ALGAINP VISIBLE LIGHT-EMITTING DIODES

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.

Twofold efficiency improvement in high performance AlGaInP light-emitting diodes in the 555-620 nm spectral region using a thick GaP window layer

AlGaInP light‐emitting diodes (LEDs) with external quantum efficiencies ≥6% and luminous performance of 20 lm/W have been fabricated. These LEDs are twice as efficient as previously reported AlGaInP devices throughout the spectral region from green (555 nm) to red‐orange (620 nm) owing to a thicker GaP window layer (45 vs 15 μm). Using hydride vapor phase epitaxy, thick GaP window layers were grown on top of AlGaInP double heterostructures grown by organometallic vapor phase epitaxy. The efficiency of the LEDs was found to improve as the thickness of the window layer was increased from 9 to 63 μm. This improvement is predicted by a simple model that considers the benefit of enhanced emission through the sides of the thick window. The effect of emission wavelength on quantum efficiency and luminous performance for AlGaInP LEDs with a 45 μm thick window has been studied.

Hall-effect characterization of III–V nitride semiconductors for high efficiency light emitting diodes

Abstract Variable-temperature Hall-effect measurements were employed to optimize doping for GaN layers utilized in blue, blue-green and green light emitting diodes (LEDs). N-type doping was accomplished by doping with Si, Ge, and O, and the electronic properties of these donors were studied. Si and Ge, which substitute for Ga, are shallow donors with almost identical activation energies for ionization (ca. 17 and ca. 19 meV, respectively, for a donor concentration of ca. 3×10 17 cm −3 ). O substitutes for N and introduces a slightly deeper donor level into the bandgap of GaN having an activation energy of ca. 29 meV (for a donor concentration of ca. 1×10 18 cm −3 ). Mg doping was employed to achieve p-type conductivity for GaN device layers. Mg substitutes for Ga introducing a relatively deep acceptor level. For the analysis of the variable-temperature Hall-effect data, it was found important to take the coulomb interaction between ionized acceptors into account, leading to lower activation energy with increasing degree of ionization (increasing temperature). The activation energy for ionization of Mg acceptors in GaN was thus estimated to be (208±6) meV for very low acceptor concentrations. Using optimized nitride layers, LEDs with typical external quantum efficiencies of ca. 10% in the blue and blue-green, and ca. 8% in the green wavelength range were achieved. Due to optimized doping, the forward voltages for these diodes were as low as 3.2 V at 20 mA drive current.

III–V Nitride semiconductors for high-performance blue and green light-emitting devices

Most of the rapid developments in (AlIn)GaN alloy system technology have occurred within the past few years, and the technology is still moving at a fast pace. New performance records for light-emitting diodes and laser diodes are constantly being reported. This article highlights the progression of the development of the (AlIn)GaN alloy system and describes the fabrication and performance of some of the light-emitting devices that have been produced to date.

Properties and use on In 0.5 (Al x Ga 1-x ) 0.5 P and Al x Ga 1-x As native oxides in heterostructure lasers

Data are presented demonstrating the formation of native oxides from high Al composition In0.5(AlxGa1-x)0.5P (x≳ 0.9) by simple annealing in a “wet” ambient. The oxidation occurs by reaction of the high Al composition crystal with H2O vapor (in a N2 carrier gas) at elevated temperatures (≥500° C) and results in stable transparent oxides. Secondary ion mass spectrometry (SIMS) as well as scanning and transmission electron microscopy (SEM and TEM) are employed to evaluate the oxide properties, composition, and oxide-semiconductor interface. The properties of native oxides of the In0.5(AlxGa1-x)0.5P system are compared to those of the AlxGa1-xAs system. Possible reaction mechanisms and oxidation kinetics are considered. The In0.5(AlxGa1-x)0.5P native oxide is shown to be of sufficient quality to be employed in the fabrication of stripe-geometry In0.5(AlxGa1-x)0.5P visible-spectrum laser diodes.

Impurity‐induced layer disordering of high gap Iny(AlxGa1−x)1−yP heterostructures

Data are presented showing the impurity‐induced layer disordering (IILD), via low‐temperature (600–675 °C) Zn diffusion, of In0.5(AlxGa1−x)0.5P quantum well heterostructures and an In0.5Al0.2Ga0.3P‐GaAs heterojunction grown using metalorganic chemical vapor deposition. Secondary ion mass spectroscopy, transmission electron microscopy, and photoluminescence are used to confirm IILD, which occurs via atom intermixing on the column III site aided by column‐III‐atom interstitials. In addition, high‐temperature anneals (800–850 °C) are performed on the same crystals to confirm the thermal stability of the heterointerfaces.

Short-wavelength (≤6400 Å) room-temperature continuous operation of p-n In0.5(AlxGa1−x)0.5P quantum well lasers

Data are presented demonstrating short‐wavelength (≲6400 A) continuous (cw) laser operation of p‐n diode In0.5(AlxGa1−x)0.5P multiple quantum well heterostructure (QWH) lasers grown lattice matched on GaAs substrates using metalorganic chemical vapor deposition. In the range from −30 °C to room temperature (RT≊300 K, λ≊6395 A) the threshold current density changes from 2.3×103 A/cm2 (−30 °C) to 3.7×103 A/cm2 (RT, 300 K). The cw 300 K photopumped laser operation of the same quaternary QWH crystal is an order of magnitude lower in threshold (7×103 W/cm2, Jeq∼2.9×103 A/cm2) than previously reported for this crystal system, and agrees with the successful demonstration of cw 300 K laser diodes at this short wavelength.

High-brightness AlGaInN light-emitting diodes

Currently, commercial LEDs based on AlGaInN emit light efficiently from the ultraviolet-blue to the green portion of the visible wavelength spectrum. Data are presented on AlGaInN LEDs grown by organometallic vapor phase epitaxy (OMVPE). Designs for high-power AlGaInN LEDs are presented along with their performance in terms of output power and efficiency. Finally, present and potential applications for high-power AlGaInN LEDs, including traffic signals and contour lighting, are discussed.

Native‐oxide stripe‐geometry In0.5(AlxGa1−x)0.5P‐In0.5Ga0.5P heterostructure laser diodes

Data are presented demonstrating the formation of stable, device‐quality native oxides from high Al composition In0.5(AlxGa1−x)0.5P (x ∼0.9) via reaction with H2O vapor (in N2 carrier gas) at elevated temperatures (≥500 °C). The oxide exhibits excellent current‐blocking characteristics and is employed to fabricate continuous room‐temperature stripe‐geometry In0.5(AlxGa1−x)0.5P‐In0.5Ga0.5P double‐heterostructure laser diodes.