Qhalid Fareed

Quaternary AlInGaN Multiple Quantum Wells for Ultraviolet Light Emitting Diodes

We report on a novel pulsed atomic layer epitaxy (PALE) growth technique for quaternary AlInGaN films for ultraviolet optoelectronics applications. Using the PALE approach, quaternary AlInGaN/AlInGaN multiple quantum wells (MQWs) were successfully grown over sapphire substrates. These were characterized using X-ray diffraction, atomic force microscopy, and photoluminescence to establish structural and optical quality. Incorporating the PALE grown quaternary MQWs as the active layer we also demonstrated ultraviolet electroluminescence at 343 nm with an output power up to 0.12 mW at room temperature.

Robust 290 nm Emission Light Emitting Diodes over Pulsed Laterally Overgrown AlN

We report 290 nm emission deep ultra-violet light emitting diodes with AlGaN multiple quantum well active regions exhibiting stable cw-powers in excess of 2 mW. For flip-chip packaged devices with an active area of 140 µm2 there was no saturation of the output powers even for DC pump currents up to 60 mA. The light emitting diodes were deposited over 17-µm-thick high-quality pulsed, laterally overgrown AlN layers over sapphire. From the on-wafer measurement of the thermal degradation of output powers, we estimated the lifetimes to be well over 5000 h. The superior performance of the reported light emitting diodes is attributed to reduced thermal impedance and a lower overall defect density in the laterally overgrown AlN.

Robust 285 nm Deep UV Light Emitting Diodes over Metal Organic Hydride Vapor Phase Epitaxially Grown AlN/Sapphire Templates

Significant progress has been made in the development of III–nitride deep UV light emitting diodes (LEDs) grown on sapphire substrates using AlGaN multiple quantum well (MQW) active regions. This progress was largely based on the advancements integrated in the first reported deep UV LEDs demonstrating sub-milliwatt output power. 1) The key to the success of these devices was based on three technical advancements. First was the use of pulsed atomic layer epitaxy (PALE) to improve the quality of the buffer AlN layer. 2,3) PALE deposited AlxGa1� xN/AlyGa1� yN shortperiod superlattices were also inserted between the buffer AlN and the n-contact AlGaN layer to control the thinfilm stress, thereby mitigating epilayer cracking. 4) Finally, a p-GaN/p-AlGaN heterojunction contact layer was used to improve hole injection. 5) The same technical approaches were subsequently used by Zhang et al. to commercialize deep UV LEDs. 6)

First Demonstration of Semipolar Deep Ultraviolet Light Emitting Diode on m-Plane Sapphire with AlGaN Multiple Quantum Wells

We report on the first demonstration of a semipolar AlGaN based deep ultraviolet (UV) light emitting diode (LED), with a peak emission wavelength of 307 nm. The LED structure was grown on an m-plane sapphire substrate using metal organic chemical vapor deposition (MOCVD). A combination of pulsed MOCVD (PMOCVD) grown AlN and a short period AlN/AlGaN superlattice structure was found to be instrumental in achieving singular semipolar structural phase of (1122) with a defect density low enough to fabricate the light emitting device. The on-wafer optical output power of the fabricated LED was ~20 µW at a dc pump current of 20 mA.

Enhancement-Mode Insulating-Gate AlInN/AlN/GaN Heterostructure Field-Effect Transistors with Threshold Voltage in Excess of +1.5 V

This letter presents the dc characteristics of normally Off AlInN/AlN/GaN metal–oxide–semiconductor heterostructure field-effect transistors (MOS-HFETs). The devices were fabricated using a recessed gate and SiON dielectric layers for gate isolation. For a device with a 1.5 µm gate length and an 8-µm-long channel, the threshold voltage was above +1.5 V and a maximum drain current density of 0.7 A/mm was reached under 6 V gate bias. These enhancement-mode MOS-HFETs have an excellent potential for power electronics applications.

280 nm Deep Ultraviolet Light Emitting Diode Lamp with an AlGaN Multiple Quantum Well Active Region

We report on room-temperature (RT) operation of a 280 nm deep ultraviolet light emitting diode lamp with monolithic micro-pixel device geometry. RT continuous-wave power as high as 42 mW was measured at a dc pump current of 1 A for a device active area of 880 µm2. For RT operation at a peak dc power of 22 mW (pump current 400 mA), the lamps packaged on TO-66 headers had a 50% power lifetime in excess of 1500 h.

Vertical Injection Thin Film Deep Ultraviolet Light Emitting Diodes with AlGaN Multiple-Quantum Wells Active Region

Vertically conducting thin film high power deep ultraviolet (DUV) light emitting diodes with peak emission wavelength of 280 nm are reported. The light emitting diodes (LEDs) were fabricated using a laser assisted lift-off process. Single chip devices exhibited a record high output power of 5.5 mW at a continuous-wave (cw) current density of only 25 A/cm2. Their lifetime is estimated to be well over 2000 h. We attribute the superior performance of the devices to reduced thermal impedance and the vertical current conduction device geometry.

Effect of Oxygen on the Activation of Mg Acceptor in GaN Epilayers Grown by Metalorganic Chemical Vapor Deposition

The effect of oxygen mixed in nitrogen on p-type activation in Mg-doped GaN epilayers grown by metalorganic chemical vapor deposition (MOCVD) was investigated. The samples annealed in N2/O2 (1%) ambient exhibited the best electrical properties with respect to hole concentration. SIMS data suggested that oxygen reacted with hydrogen present in the Mg-doped GaN samples during the thermal annealing process, thereby enhancing the activation of Mg acceptors.

REACTIVE ION ETCHING OF GAN AND ALXGA1-XN USING CL2/CH4/AR PLASMA

Reactive ion etching (RIE) of p-GaN and p-AlxGa1-xN has been investigated using Cl2/CH4/Ar plasmas in the conventional RIE technique. It has been found that variation of CH4 percentage in gas mixtures leads to changes in the etch rate of both p-GaN and p-Al0.15Ga0.85N. The maximum etch rate for p-GaN has been found to be 257 nm/min in Cl2/Ar plasma containing 2.5% CH4 and the value is 170 nm/min for p-Al0.15Ga0.85N in Cl2/Ar plasma containing 10% CH4. With increasing rf power, the etch rates for p-GaN and p-Al0.15Ga0.85N reach as high as 433 nm/min and 255 nm/min respectively. Under optimum conditions of gas composition, radiofrequency (rf) power, and temperature, an anisotropic and smooth etch profile is obtained. The etched surface exhibits small roughness.

Selective fabrication of InGaN nanostructures by the focused ion beam/metalorganic chemical vapor deposition process

In the present article we report on the selective fabrication of InGaN nanostructures on Si coated GaN/sapphire substrates using the focused ion beam (FIB)/metalorganic chemical vapor deposition (MOCVD) process. InGaN quantum dots and InGaN quantum wires have been fabricated. The process combines window openings in the Si mask layer with localized highly energetic Ga+ FIB irradiation, subsequent photo-assisted wet chemical etching in a solution of KOH:H2O2 (3:1 by mole) and finally the growth of InGaN/GaN nanostructures using MOCVD. This technique proved to be efficient in realizing practically damage-free etching, hence preventing the deterioration of the nanostructure’s crystal quality. The density, size, and positions of the nanostructures could be well designed and controlled using the above process. Structural characterization by transmission electron microscopy, atomic force microscopy observations, and optical investigation by cathodoluminescence were carried out.