Jone-Fang Chen

InGaN-AlInGaN multiquantum-well LEDs

InGaN-GaN and InGaN-AlInGaN multiquantum-well (MQW) light-emitting diodes (LEDs) were both fabricated and their optical properties were evaluated by photoluminescence (PL) as well as electroluminescence (EL). We found that the PL peak position of the InGaN-AlInGaN MQW occurs at a much lower wavelength than that of the InGaN-GaN MQW. The PL intensity of the InGaN-AlInGaN MQW was also found to be larger. The EL intensity of the InGaN-AlInGaN MQW LED was also found to be larger than that of the InGaN-GaN MQW LED under the same amount of injection current. Furthermore, it was found that EL spectrum of the InGaN-AlInGaN MQW LED is less sensitive to the injection current. These observations all suggest that we can improve the properties of nitride-based LEDs by using AlInGaN as the barrier layer.

GaN metal-semiconductor-metal ultraviolet sensors with various contact electrodes

Indium-tin-oxide (ITO), Au, Ni, and Pt layers were deposited onto n-GaN films and/or glass substrates by electron-beam evaporation. With proper annealing, it was found that we could improve the optical properties of the ITO layers and achieve a maximum transmittance of 98% at 360 nm. GaN-based MSM UV sensors with ITO, Au, Ni, and Pt as contact electrodes were also fabricated. It was found that we could achieve a maximum 0.12 A photocurrent and a photocurrent to dark current contrast higher than five orders of magnitude for the 600/spl deg/C-annealed ITO/n-GaN MSM UV sensor at a 5-V bias voltage. We also found that the maximum responsivity at 345 nm was 7.2 A/W and 0.9 A/W when the 600/spl deg/C-annealed ITO/n-GaN MSM UV sensor was biased at 5 V and 0.5 V, respectively. These values were much larger than those observed from other metal/n-GaN MSM UV sensors. However, the existence of photoconductive gain in the 600/spl deg/C-annealed ITO/n-GaN MSM UV sensor also results in a slower operation speed and a smaller 3-dB bandwidth as compared with the metal/n-GaN MSM UV sensors.

Growth of nanoscale InGaN self-assembled quantum dots

It has been demonstrated that we can use interrupted growth mode in metalorganic chemical vapor deposition (MOCVD) to fabricate nanoscale InGaN self-assembed quantum dots (QDs). With a 12-s growth interruption, we successfully formed InGaN QDs with a typical lateral size of 25 nm and an average height of 4.1 nm. The QDs density is about 2 x 10(10) cm(-2). In contrast, much larger InGaN QDs were obtained without growth interruption. Compared with samples prepared without growth interrupt, a much larger photoluminescence (PL) intensity and a large 67meV PL blue shift was observed from samples prepared with growth interrupt. These results suggest such a growth interrupt method is potentially useful in nitride-based optoelectronic devices grown by MOCVD

Si and Zn co-doped InGaN-GaN white light-emitting diodes

InGaN-GaN double heterostructure (DH) and multiquantum-well (MQW) light-emitting diodes (LEDs) with Si and Zn co-doped active well layers were prepared by metalorganic chemical vapor deposition (MOCVD). It was found that we could observe a broad long-wavelength donor-acceptor (D-A) pair-related emission at 500/spl sim/560 nm. White light can thus be achieved by the combination of such a long-wavelength D-A pair emission with the InGaN band-edge-related blue emission. By increasing the DMZn mole flow rate to 360 nmole/min, we could achieve a Si and Zn co-doped In/sub 0.3/Ga/sub 0.7/N-GaN MQW LED with color temperature of 4100 K, color rendering index of 70, and color coordinates x=0.383, y=0.405. It was also found that the 20-mA forward voltage and the breakdown voltage of such Si and Zn co-doped In/sub 0.3/Ga/sub 0.7/N-GaN MQW LEDs were both smaller than those of the conventional phosphor-converted white LEDs.

Effects of gate bias on hot-carrier reliability in drain extended metal-oxide-semiconductor transistors

The effect of gate voltage on hot-carrier induced degradation in drain extended high-voltage metal-oxide-semiconductor (MOS) transistors with thick gate oxide (100nm) structure is presented. Different from the conventional low-voltage n-type MOS transistors, under a fixed drain voltage, devices stressed at a higher Vgs result in a greater maximum transconductance and on-resistance degradation. Under higher Vgs, the increase in channel hot-carrier injection is responsible for the greater Gm,max degradation. On the other hand, Kirk effect induced increase in drain avalanche hot carriers near the drain as well as higher electric field in the channel is responsible for the greater Ron degradation.

High Brightness Green Light Emitting Diode with Charge Asymmetric Resonance Tunneling Structure

In this work, we have applied the so called charge asymmetric resonance tunneling (CART) structure to nitride-based green light emitting diode (LED). From our CART LED, we observed an abrupt turn-on voltage near 2.2 V, and the forward voltage is around 3.2 V at 20 mA injection current. At 20 mA, the output power, and external quantum efficiency of the CART LED are about 4 mW, and 6.25%, respectively. The high brightness and efficiency green LED can be obtained by using the CART structure.

4H-SiC metal-semiconductor-metal ultraviolet photodetectors with Ni/ITO electrodes

Abstract Indium–tin-oxide (ITO), Ni/ITO and Ni layers were deposited onto glass and/or SiC substrates by DC sputtering under different deposition conditions. SiC-based metal–semiconductor–metal (MSM) ultraviolet (UV) photodetectors were also fabricated using these materials as contract electrodes. It was found that ITO film deposited without oxygen gas could provide us a better optical property and a better electrical property. It was also found that the dark current of the ITO/SiC MSM UV photodetector was extremely large. Furthermore, it was found that the insertion of a 10 nm Ni layer could significantly reduce the dark current. It was also found that the photo-current to dark current contrast was more than 3 orders of magnitude with a 5 V applied bias for the SiC MSM UV photodetector with 10 nm Ni/90 nm ITO contact electrodes. With an even larger 40 V applied bias, the photo-current to dark current contrast could almost reach 4 orders of magnitude.

Improvement of electrical and reliability properties of tantalum pentoxide by high-density plasma (HDP) annealing in N 2 O

This study aims to improve the electrical characteristics and reliability of low-pressure chemical vapor deposited (LPCVD) tantalum pentoxide (Ta/sub 2/O/sub 5/) films by a new post-deposition annealing technique using high-density plasma (HDP). Experimental results indicate that excited oxygen atoms generated by N/sub 2/O decomposition from HDP annealing can effectively reduce the carbon and hydrogen impurity concentrations and repair the oxygen vacancies in the as-deposited CVD Ta/sub 2/O/sub 5/ film, thereby resulting in a remarkable reduction of the films leakage current. Two other post-deposition annealing conditions are compared: HDP O/sub 2/ annealing and conventional plasma O/sub 2/ annealing. The comparison reveals that HDP N/sub 2/O annealing has the lowest leakage current and superior time-dependent dielectric breakdown (TDDB) reliability.