S.-R. Jeon

Ultraviolet light-emitting diodes operating in the 340nm wavelength range and application to time-resolved fluorescence spectroscopy

We report on the development of UV light-emitting diodes in the 340nm wavelength range, based on quaternary AlGaInN quantum-well active media. Output powers up to 1mW from small area devices (<100μm diameter) directly off a planar chip have been achieved. The devices have been operated as subnanosecond pulsed sources to demonstrate their applicability to compact time-resolved fluorescence spectroscopy.

Investigation of Mg doping in high-Al content p-type AlxGa1−xN (0.3<x<0.5)

A study of Mg doping of AlxGa1−xN up to x∼50% using microstructural and electrical probes is reported. The viability of effective p-type doping is defined by a minimum concentration of Mg required to offset the background impurities and, more importantly, a maximum limit above which inversion domains and structural defects start to nucleate, accompanied by a rapid degradation of electrical transport. Resistivity of 10 Ω cm and free hole concentrations above 1017cm−3 are achieved for AlxGa1−xN up to x∼50% within an optimum window of Mg incorporation.

Droplet heteroepitaxy of GaN quantum dots by metal-organic chemical vapor deposition

Optically active GaN quantum dots on conductive AlGaN templates are synthesized by droplet heteroepitaxy, whereby the Ga droplets are converted to GaN islands in the presence of ammonia at 600°C. We have investigated the evolution of metallic Ga layers on AlGaN, obtaining the optimal surface densities and size distribution of the Ga droplets. The stability of GaN islands is influenced by the surface kinetics and the initial droplet size; the condition of Ga deposition and subsequent nitrogen exposure is identified, which preserves the initial density of the Ga droplets. A nitrogen-rich environment is identified as a necessary condition for maintaining the optimal GaN morphology by suppressing the Ga surface diffusion and preventing two-dimensional layer growth.

High Performance AlGaInN Ultraviolet Light-Emitting Diode at the 340 nm Wavelength

We report on high output power from the quaternary AlGaInN multiple quantum well (MQW) ultraviolet light emitting diodes (UV LEDs) in the 340 nm wavelength range. The output power up to 1.5 mW from a 100 µm diameter device with bare-chip configuration was measured under room temperature cw operation. The internal quantum efficiency was estimated to be between 7 and 10%. In addition, the output power and external quantum efficiency for fully packaged 1×1 mm2 large area device were as high as 54.6 mW and 1.45%, respectively, at the injection current of 200 A/cm2 under pulsed operation. The devices were incorporated into prototype system for fluorescence based bio-sensing as excitation source.

Growth, Characterization, and Application of High Al-content AlGaN and High Power III-Nitride Ultraviolet Emitters

A study of Si-doped and Mg-doped Al x Ga 1-x N up to × ∼ 50 % and the characteristics of ultraviolet (UV) light emitting diodes (LEDs) with emission wavelengths at 340 nm and 290 nm are reported. By using grading super-lattices (SLs) before n-type AlGaN growth, surface roughness is much improved. Resistivity of 2.9×10- 2 Ωcm and free electron concentrations of 2.9×10 cm- are achieved for n-type Al 0.45 Ga 0.55 N. The viability of effective p-type doping is defined by a minimum concentration of Mg required to offset the background impurities and, more importantly, a maximum limit above which inversion domains and structural defects start to nucleate, accompanied by a rapid degradation of electrical transport. Resistivity of 10 Ωcm and free hole concentrations above 10 17 cm −3 are achieved for Al x Ga 1-x N up to × ∼ 50 % within an optimum window of Mg incorporation. Output powers up to 1.5 mW from small area 340 nm LEDs ( 2 device area and 0.52 mm 2 mesa area), output power of 79 mW from 340 nm LEDs and 8.5 mW from 290 nm LEDs are achieved under pulse mode (1kHz, 2% duty factor).

Performance and application of high power ultraviolet AlGaInN light emitting diodes

We report on high output power from the quaternary AlGaInN multiple quantum well (MQW) ultraviolet light emitting diodes (UV LEDs) in the 340 nm and 280 nm wavelength range. The output power up to 1.5 mW from a 100 μm diameter device with bare-chip configuration was measured under room temperature cw operation. The internal quantum efficiency was estimated to be between 7 and 10%. In addition, the output power and external quantum efficiency for fully packaged 1x1mm2 large area device were as high as 54.6 mW and 1.45%, respectively, at the injection current of 200 A/cm2 under pulsed operation. The devices were incorporated into prototype system for fluorescence based bio-sensing. We also report the performance of 285 nm UV LEDs.