This work investigates the effect of Cl 2 / Ar dry etching on p-GaN. The root-mean-square ͑rms͒ surface roughness is measured, and the depth display ͑Bearing analysis͒ is monitored. The current-voltage characteristics of etched p-GaN with Ni ͑20 nm͒ /Au ͑20 nm͒ metallization are studied. Experimental results indicate that the etching rate does not increase significantly with the Cl 2 flow rate at a constant power or chamber pressure. The Bearing ratio data exhibit a much stronger variation with etch conditions, the rms displays the same trend but to a lesser extent.

This work investigates the temperature dependence of the current-voltage (I-V) characteristics of n-ZnO∕p-GaN junction diodes. The n-ZnO films were deposited on top of the p-GaN by dc sputtering with subsequent annealings at 500, 600, 700, and 800°C for 60s. The Hall measurement and the x-ray diffraction pattern are measured to study the n-ZnO films. The temperature sensitivity coefficients of the I-V characterizations are obtained by different substrate temperatures (25, 50, 100, and 150°C) and the extracted values are 2.10, 1.93, 3.22, and 1.36mV∕°C in the forward bias and 8.7, 8.0, 4.6, and 2.3mV∕°C in the reverse bias, respectively. The fabricated n-ZnO∕p-GaN diode with ZnO annealing temperatures at 800°C demonstrates the lowest temperature dependence.

This study investigated the temperature dependence of the current-voltage (I-V) characteristics of Al-doped MgxZn1-xO/p-AlGaN junction diodes. The n-type Al-doped MgxZn1-xO (AMZO) films were deposited on p-AlGaN using a radio-frequency (rf) magnetron sputtering system followed by annealing at 700, 800, and 900°C in a nitrogen ambient for 60 s. The n-AMZO/p-AlGaN diode at a substrate temperature of 25°C showed the lowest leakage current in reverse bias. The n-AMZO/p-AlGaN diode with an AMZO annealed at 900°C demonstrated the lowest reverse leakage current. The temperature sensitivity coefficients of the I-V characterizations were obtained at different substrate temperatures (25, 50, 75 100, and 125°C), providing extracted values of 6.4, 7.6, and 5.6 mV/°C in forward bias and −20, 5.6, and 0.8 mV/°C in reverse bias for the AMZO films annealed at 700, 800, and 900°C, respectively. The n-AMZO/p-AlGaN junction diode fabricated with AMZO annealed at 900°C demonstrated the lowest temperature dependence. In addition, the light emission was derived from the forward-biased junction, and near-ultraviolet light emission was evident at all of the p-n diodes. Based on these findings, the n-AMZO/p-AlGaN diodes are suitable for GaN-based heterojunction bipolar transistors (HBTs) and near-ultraviolet light-emitting diodes (LEDs).

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This letter investigates three composite metals used as a reflector and Ohmic contact on n-GaN to simplify the process in a flip-chip light-emitting diode (FCLED). The investigated composite metals were Ti∕Al∕Ti∕Au, Cr∕Al∕Cr∕Au, and Cr∕Ti∕Au. The specific contact resistivities of the Ti∕Al∕Ti∕Au, Cr∕Al∕Cr∕Au, and Cr∕Ti∕Au Ohmic contacts on n-GaN were changed from 1.4×10−4, 1.7×10−4, and 1.9×10−4Ωcm2 to 1.3×10−4, 1.1×10−4, and 3.3×10−5Ωcm2, respectively, after 500h of thermal stress. The corresponding operating voltages of FCLEDs with different composite metals were changed by less than 1%. After 96h of thermal stress, the luminous intensities of the three structures decreased by 6.2%, 11.1%, and 1.4%, respectively. The GaN FCLED that was fabricated with Cr∕Ti∕Au as a reflector and an Ohmic contact on n-GaN exhibits good thermal stability and luminous intensity.

Niobium-doped Mg x Zn 1−x O (Nb-MZO) mixed oxide films with high transmittance were successfully deposited on sapphire substrates through radio-frequency (RF) magnetron sputtering using a 4-in ZnO/MgO/NbO x (75/20/5 wt%) target. In this study, the films were analyzed using Hall measurements, X-ray diffraction (XRD), transparent performance measurements, and X-ray photoelectron spectroscopy (XPS). XRD results showed two peaks: MgO 2 ( 002)-wurtzite and Mg x Zn 1−x O (111)-cubic peaks. The Nb-MZO films exhibited high transparency, with transmittance exceeding 90% in the visible region and a sharp absorption edge in the ultraviolet (UV) region, implying that the MgO content in the Nb-MZO layer increased the bandgaps. These results indicate that Nb-MZO films are ideal for use as transparent contact layers in near-UV light-emitting diodes. Hall measurements and XPS results successfully demonstrated the p-type conductivity of the Nb-MZO films because of the composition of the N-Nb binding caused by annealing in nitrogen atmosphere.

This work presents dc characteristics (gain and leakage current) of a GaN/InGaN/ZnO npn collector-up heterojunction bipolar transistor (HBT) measured at 300, 200, and 100 K. The GaN-based epilayers of HBT were grown by metallorganic chemical vapor deposition, and the n-ZnO film was then deposited on top of p-InGaN by sputtering. X-ray diffraction analysis demonstrates that annealing at 600°C for 60 s in ambient normalN2 improved the quality of the ZnO film. Moreover, this study shows that the current gains (β) from the Gummel plot increased as the temperature decreased because the leakage current of the collector current (InormalC) is not a strong function of temperature. However, gains (GCE) from the measured common-emitter current–voltage characteristics increased slightly as the temperature decreased due to a reduction in the recombination current coupled with lower injection efficiency. These preliminary results show the potential of fabricating GaN/InGaN/ZnO HBTs without dry etching to reach the p-GaN layer, as required in the emitter-up geometry.