Chun-Kai Wang

Photo-CVD SiO/sub 2/ layers on AlGaN and AlGaN-GaN MOSHFET

High-quality SiO/sub 2/ was successfully deposited onto AlGaN by photochemical vapor deposition (photo-CVD) using a D/sub 2/ lamp as the excitation source. The resulting interface state density was only 1.1 /spl times/ 10/sup 11/ cm/sup -2/eV/sup -1/, and the oxide leakage current was dominated by Poole-Frenkel emission. Compared with AlGaN-GaN metal-semiconductor HFET (MESHFETs) with similar structure, the gate leakage current is reduced by more than four orders of magnitude by using the photo-CVD oxide layer as gate oxide in AlGaN-GaN metal-oxide-semiconductor heterojunction field-effect transistors (MOSHFETs). With a 2-/spl mu/m gate, the saturated I/sub ds/, maximum g/sub m/ and gate voltage swing (GVS) of the fabricated nitride-based MOSHFET were 572 mA/mm, 68 mS/mm, and 8 V, respectively.

GaN-Based Light-Emitting Diode With Sputtered AlN Nucleation Layer

The crystal quality, electrical, and optical characteristics of GaN-based light-emitting diodes (LEDs) were improved using a sputtered AlN nucleation layer. Replacing the in situ AlN nucleation layer with the sputtered AlN nucleation layer reduced the (002) and (102) X-ray rocking curve widths of the GaN layer from 318.0 to 201.1 and 412.5 to 225.0 arcsec, respectively. The -20-V reverse leakage current of the LEDs with the sputtered AlN nucleation layer is about three orders less than that of the LEDs with the in situ AlN nucleation layer. In addition, the LEDs with sputtered AlN nucleation layer could sustain more than 60% passing yield on the ESD test of under a -600-V machine mode, whereas the LEDs with the in situ AlN nucleation layer sustained less than 40% passing yield. Moreover, the 20-mA output power of the LEDs with the sputtered AlN nucleation layer also improved by approximately 5.73% compared with that of the LEDs with the in situ AlN nucleation layer.

The thickness effect of p-AlGaN blocking Layer in UV-a bandpass photodetectors

By means of 60-, 150-, and 300-nm-thick blocking p-Al/sub 0.1/Ga/sub 0.9/N layers, we have successfully achieved high performance on nitride-based p-i-n bandpass photodetectors. The peak responsivities were estimated to be 0.131, 0.129, and 0.13 A/W at 354, 357, and 356 nm for 60-, 150-, and 300-nm-thick p-Al/sub 0.1/Ga/sub 0.9/N blocking layer, respectively, corresponding to a quantum efficiency of around 46%. Moreover, spectral responsivity for 300-nm-thick blocking p-Al/sub 0.1/Ga/sub 0.9/N layer shows the narrowest bandpass characteristics from 320 to 365 nm (UV-A region). The photodetectors exhibit a 20-V break-down voltage and a small dark current of around 3 pA at 5-V reverse bias. For our 330 /spl times/ 330 /spl mu/m/sup 2/ devices given bias of 0 V, the detectivity D/sup */ limited by Johnson noise are calculated to be 3.43 /spl times/ 10/sup 13/, 6.77 /spl times/ 10/sup 13/, and 8.22/spl times/10/sup 13/ cm/spl middot/Hz/sup 0.5/W/sup -1/, respectively.

High Temperature Performance and Low Frequency Noise Characteristics of AlGaN/GaN/AlGaN Double Heterostructure Metal-Oxide-Semiconductor Heterostructure Field-Effect-Transistors with Photochemical Vapor Deposition SiO2 Layer

High quality SiO2 films were successfully deposited onto AlGaN using photochemical vapor deposition (photo-CVD). The interface state density, Dit, of photo-CVD SiO2 was estimated to be only 1.1×1011 cm-2eV-1 at room temperature and still only 3.5×1012 cm-2eV-1 even at 175°C. With a 1 µm gate length, it was found that the maximum saturated drain-source current (Ids), maximum transconductance (gm) and gate voltage swing (GVS) of the AlGaN/GaN/AlGaN double heterostructure metal-oxide-semiconductor heterostructure field-effect-transistors (MOS-HFETs) fabricated were 755 mA/mm, 95 mS/mm and 8 V, respectively. Even at 300°C, the maximum saturated Ids and maximum gm of the MOS-HFETs fabricated were still kept at 527 mA/mm and 77 mS/mm, respectively. Furthermore, from the low frequency noise power spectrum, it was found that noise power density of the AlGaN/GaN/AlGaN double heterostructure was lower and presented pure 1/f noise with smaller trapping effects than conventional structures.

Noise Analysis of Nitride-Based Metal-Oxide-Semiconductor Heterostructure Field Effect Transistors with Photo-Chemical Vapor Deposition SiO2 Gate Oxide in the Linear and Saturation Regions

Low frequency noise of AlGaN/GaN metal–oxide–semiconductor heterostructure field effect transistors (MOS-HFETs) with photo-chemical vapor deposition (photo-CVD) SiO2 gate oxide was investigated as functions of gate bias (from Vgs=-6 to 4 V) both in the linear (Vds=3 V) and saturation (Vds=12 V) regions. In the linear region, it was found the measured noise spectra were fitted well by the 1/ f law up to 1 kHz. The normalized noise power density of the MOS-HFETs was proportional to Vgs-1 when -4<Vgs<0 V, and was independent of the gate voltage when 0<Vgs<4 V. The Hooges coefficient α was estimated to be around 10-3. In the saturation region, it was found that the measured noise power density decreased monotonically with the increase of gate voltage.

High transconductance AlGaN/GaN MOSHFETs with photo-CVD gate oxide

High quality SiO2 was successfully deposited on GaN by photochemical vapour deposition (photo-CVD) using a D2 lamp as the excitation source. It was found that the interface state density was only 8.4 × 1011 cm−2 eV−1 for photo-CVD SiO2 layers on GaN prepared at 300 °C. AlGaN/GaN metal–oxide–semiconductor heterojunction field effect transistors were fabricated with photo-CVD oxide as the insulating layer. It was found that room temperature saturation Ids, maximum gm and gate voltage swing of the devices were 1220 mA mm−1, 240 mS mm−1 and 4.5 V, respectively. Even at an evaluated temperature of 300 °C, the device still exhibits the maximum transconductance of 180 mS mm−1.

Synthesis and characterization of poly(2,2′-diphenylbiphenyl-4,4′-ylenevinylene-2″,5″-bis(trimethylsilyl)-para-phenylenevinylene), a new efficient blue-light emitting polymer

Abstract The synthesis and application of poly(2,2′diphenylbiphenyl-4,4′-ylenevinylene-2″,5″-bistrimethylsilyl- para -phenylenevinylene) (DPBP-PPV), a novel blue-light emitting polymer is reported. The EL spectrum of DPBP-PPV is almost identical with its PL spectrum. By blending with PBD, the devices show a high external efficiency of 0.2% with the highest brightness of 300 cd m −2 .

Effect of Varied Undoped GaN Thickness on ESD and Optical Properties of GaN-Based LEDs

The optical property and electrostatic discharge (ESD) endurance of GaN-based light-emitting diodes (LEDs) with varied undoped GaN thickness are studied and demonstrated. As the undoped GaN thickness increased, the generation of V-shaped defects in the active region was suppressed. Therefore, the output power for a 6-μ.m-thick undoped GaN layer would be enhanced remarkably due to the reduction of nonradiative recombination ratio within the active region. On the other hand, under a reverse ESD pulse voltage of 5.5 kV, the survival rate of the LEDs with an undoped GaN layer thickness of 1.5, 4, and 6 μm were 75%, 65%, and 55%, respectively. It was found that the ESD endurance for a 1.5-μ.m-thick undoped GaN layer with higher internal capacitance was obviously better than others. This could be related to the built-in electric field of LEDs induced by spontaneous polarization field.

Leakage Current Analysis of Nitride Based Optoelectronics by Emission Microscopy Inspection

GaN MSM photodetectors (PDs) and p-i-n photodetectors (PDs) with E-gun SiO2 passivation and plasma enhanced chemical vapor deposited (PECVD) SiO2 passivation were fabricated and characterized. Inductance couple plasma (ICP) etching would cause significant damage on GaN MSM photodetectors. The damage was proved to induce leakage current via the surface of device by using emission microscopy inspection. However, the surface damage can be partially recovered by E-gun SiO2 passivation. As for the passivation for p-i-n photodetectors, the effect is not significant in the reduction of dark current due to smaller etched area as compare to the whole area of p-i-n PDs.

Reducing the Current Crowding Effect on Nitride-Based Light-Emitting Diodes Using Modulated P-Extension Electrode Thickness

In this paper, nitride-based light-emitting diodes (LEDs) with the modulated thickness of p-extension electrode were proposed and fabricated. The current crowding is always occurred in the end of p-extension electrode. Thus, the resistance of p-extension electrode will be increased by reducing its thickness to prevent current crowding. The modulated thickness of p-extension electrode can be employed to enhance the light output power and reduce overall operated temperature. Compared to the conventional LED, the enhancement in light output power is 13.9% at 150 mA and the reduction in average operated temperature is about 14.6% at 80 mA. Regarding the characteristics of electrostatic discharge (ESD), the failure mode of new electrode design occurred on the terminal of thick p-extension electrode rather than current crowding region.