Plan-view transmission electron microscopy (TEM) and cathodoluminescence (CL) images were taken for the same sample at exactly the same location in n-type GaN grown on sapphire substrate by metalorganic chemical vapor deposition (MOCVD). There was a clear one to one correspondence between the dark spots observed in CL images and the dislocations in TEM foils, indicating that the dislocations are non-radiative recombination centers. The hole diffusion length in n-type GaN was estimated to be neighboring 50 nm by comparing the diameters of the dark spots in thick samples used for CL and samples that were thinned for TEM observation. The efficiency of light emission is high as long as the minority carrier diffusion length is shorter than the dislocation spacing.

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Investigations of the new metal scheme for ohmic contact to p-GaN have been carried out. The specific contact resistance was measured to be ρc=3.6×10-3 Ω cm2 which is the lowest value ever reported for moderately doped p-GaN (4.4×1017/cm3). All metals were deposited on metalorganic chemical vapour deposition (MOCVD) grown p-GaN. The interaction mechanism between Ni and p-GaN has been investigated. Zn diffusion has been observed during annealing in Au–Zn/Ni on p-GaN. The interfacial reaction mechanism during annealing has been studied by secondary ion mass spectroscopy (SIMS) measurement. From this measurement, it is observed that Ni dissociates at the p-GaN surface and this dissociation promotes the Zn diffusion upon heat treatment. The electrical properties were studied using current–voltage (I–V) measurements at room temperature. The microstructure between the Ni and p-GaN interface was investigated using high-resolution transmission electron microscopy (TEM) before and after the heat treatment.

We have grown blue (480 nm) nitride semiconductor light emitting diodes (LEDs) by plasma-assisted molecular beam epitaxy (MBE) on GaN templates. Packaged devices exhibited output powers up to 0.87 mW at 20 mA forward current. The corresponding external quantum efficiency was 1.68%. Utilizing a combination of direct current (dc) and pulsed electroluminescence measurements it has been demonstrated that at low (<20 mA) dc conditions the emission from these devices is governed by the combined effects of bandfilling and screening of electrostatic fields. However, at larger currents device heating dominates the emission properties.

Design and fabrication of monolithic blue LED series arrays that can be operated under high ac voltage are described. Several LEDs, such as 3, 7, and 20, are connected in series and in parallel to meet ac operation. The chip size of a single device is 150 μm × 120 μm and the total size is 1.1 mm × 1 mm for a 40 (20 + 20) LED array. Deep dry etching was performed as device isolation. Two‐layer interconnection and air bridge are utilized to connect the devices in an array. The monolithic series array exhibit the expected operation function under dc and ac bias. The output power and forward voltage are almost proportional to LED numbers connected in series. On‐wafer measurement shows that the output power is 40 mW for 40 (20 + 20) LED array under ac 72 V.

The compositional inhomogeneity of the InGaN layers in GaN/InGaN/GaN double-hetero (DH) and InGaN/GaN single-hetero (SH) structures grown by metalorganic chemical vapor deposition (MOCVD) on sapphire (0001) and bulk GaN was investigated by means of cathodoluminescence (CL) and energy dispersive X-ray (EDX) spectroscopy. Dotlike CL image of the band edge emission from InGaN was observed. The bright spots were found to have higher indium content compared to that on the outside of the spots. The compositional inhomogeneity increased and the density of the spot decreased with increasing film thickness. Hexagonal hillocks, which had higher indium content and emitted stronger CL, were observed on the surface of the SH structure. Compositional inhomogeneity of homoepitaxial InGaN on bulk GaN substrate was much less compared to that of InGaN on sapphire revealing that dislocation plays a key role in producing an inhomogeneity. A possible mechanism that explains these phenomena is proposed.

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