Chong-Long Ho

Planar InGaAs p-i-n Photodiodes With Transparent-Conducting-Based Antireflection and Double-Path Reflector

In this letter, we report on the design of large-area planar InP/InGaAs/InP heterostructure p-i-n photodiodes (PIN-PDs) with gallium-doped zinc oxide (GZO)/SiOx antireflective bilayer and AuGe/Au double-path reflectors for the enhancement in the position sensitivity and device response. The heavily GZO layer was grown on top of the InGaAs PIN-PDs by plasma-mode atomic layer deposition to improve the lateral resistance effect. The GZO/SiOx antireflection (AR) exhibits an average optical reflectance of below 5% in the infrared (IR) spectrum. Then, the combination of two features of AR coating and double-path reflector is employed to decrease incident light loss and increase double-path absorption. The dark current is less than several nanoamperes and the breakdown voltage is higher than 40 V reverse bias for the large-area InGaAs diode with 750- μm-diameter region. The device responsivity is 1.0 and 1.2 A/W at 1310-and 1550-nm wavelengths, respectively. Under the light illumination of 1550-nm wavelength, the photosensitivity shows good uniformity in the light-received area. The quantum efficiency is higher than 90% in the whole IR region, and the cutoff wavelength is 1650 nm.

High-Frequency Modulation of GaAs/AlGaAs LEDs Using Ga-Doped ZnO Current Spreading Layers

In this letter, we report the high-frequency modulation of GaAs/AlGaAs near-infrared (NIR) light-emitting diodes (LEDs) with gallium-doped zinc oxide (GZO) prepared by atomic layer deposition as a current spreading layer. This report analyzes the effects of aperture area of the NIR LEDs on minority carrier lifetime and further investigates the required injection current to achieve the 3-dB frequency bandwidth of 100 MHz. At the same injection current density, the LEDs with different aperture areas always exhibit the same minority carrier lifetime, which is inversely proportional to the square root of current density. It means that the GZO layer plays a good current spreading in the lateral direction from the ohmic contact of NIR LEDs, which shows the lower contact resistance and lower forward voltage.

DLTS Analyses of GaN p-i-n Diodes Grown on Conventional and Patterned Sapphire Substrates

In this letter, we report the electrical characteristics of current-voltage, capacitance-voltage, and deep-level transient spectroscopy on the GaN p-i-n diodes with a 5- μm i-layer, which were grown on the conventional sapphire substrates (CSSs) and patterned sapphire substrates (PSSs) by metal-organic chemical vapor deposition. The GaN p-i-n diodes with PSS exhibit a wider diffusion region in the forward bias, two traps at 0.43 and 0.87 eV above the valence band, and a low trap concentration of ~ 5×1016 cm-3, as compared with the GaN p-i-n diodes with CSS. These results show that the GaN p-i-n diodes grown on PSS have a better quality of epitaxial layers than those grown on CSS.

Large-Area Planar Wavelength-Extended InGaAs p-i-n Photodiodes Using Rapid Thermal Diffusion With Spin-On Dopant Technique

In this letter, we report the large-area planar-type 2.2-μm wavelength-extended InAsP/InGaAs/InAsP p-i-n photodetectors (PDs) using the rapid thermal diffusion (RTD) technique. The zinc-phosphorous-dopant-coating was used as the spin-on dopant source, which was driven into the InAsP/InGaAs heterostructure to form the p-type cap layer of p-i-n diode through the RTD process. The Si/Al₂O₃ bilayers were deposited as the antireflective coating to improve the responsivity of vertically illuminated the PDs. The 800-μm-diameter PD exhibits a low dark current of 4.1 × 10^-8 A (8.2 × 10^-6 A/cm²) at -10 mV, a cutoff wavelength of 2.2 μm, a quantum efficiency of above 90% in the wavelength range of 1.4-2.0 μm, and a high responsivity of 1.45 A/W at 2-μm wavelength at room temperature. In addition, the PD exhibits good uniformity in the light received area in the illuminated power range of 0.1-2.0 mW.

Large-Area Planar InGaAs p-i-n Photodiodes With Mg Driven-in by Rapid Thermal Diffusion

Conventional InP/InGaAs/InP heterostructure p-i-n photodiodes (PIN-PDs) are usually fabricated by postgrowth Zn diffusion to form the p-type region. In this letter, we propose a novel method to fabricate the high performance of largearea planar InP/InGaAs/InP PIN-PDs with Mg driven-in process. The Mg driven-in is implemented by spin-on dopant technique using magnesium-silica-film (MgSiOx) source and through the rapid thermal diffusion. The preparation of MgSiOx source carrier as the p-type dopant for InP/InGaAs heterostructure is more time-saving than that of zinc-phosphorous-dopant-coating because the latter needs an additional step of oxygen (O2) plasma to remove a thick resin layer. To improve the responsivity of vertically illuminated PDs, Si/Al2O3 bilayers are deposited as the antireflective coating. The 800-μm-diameter PD with Mg driven-in exhibits a low dark current of 20 pA (or 4 nA/cm2) at -10 mV, a high responsivity of 1.14 A/W at 1550-nm wavelength, an excellent quantum efficiency of 91%, and a good uniformity in the light received area. These characteristics are comparable to those of the PD with Zn driven-in.

Highly Uniform Photo-Sensitivity of Large-Area Planar InGaAs p-i-n Photodiodes With Low Specific Contact Resistance of Gallium Zinc Oxide

In this letter, we report the large-area planar-type InGaAs p-i-n photodiodes (PDs) by using gallium-doped zinc oxide (GZO) transparent conducting oxide as a lateral carrier-conducting layer for reduction in the lateral resistance of p⁺-InP contact layer and improvement in the uniformity of photo-sensitivity. After the 400 °C post-annealing, the GZO/p⁺-InP contact exhibits an ohmic characteristic and a low specific contact resistance of 8.2 × 10^-4 Ω · cm² with the transmittance over 85% in the wavelength range of 0.90-1.65 μm. The 800-μm-diameter PD exhibits a low dark current of 24 pA (5 nA/cm²) at -10 mV, a cutoff wavelength of 1.65 μm, a photo-responsivity of 1 A/W at the wavelength of 1.55 μm, and a quantum efficiency of ~80% in the wavelength range of 1-1.55 μm. In addition, the photo-sensitivity of PD in the light-received area exhibits highly uniformity even under high optical power. It is attributed to the use of GZO film as a lateral carrier-conducting layer.

Schottky Barrier Height Reduction at Interface Between GZO Transparent Electrode and InP/InGaAs Structure by Zinc Driven-in Step and Nickel Oxide Insertion

In this letter, we report the characteristics of transparent Ga-doped ZnO (GZO) electrodes contacted to the InP/InGaAs epitaxial structure both with and without a NiO_x inserting layer. The GZO films deposited onto the p-InP/InGaAs structure by both radio-frequency sputtering and plasma-mode atomic layer deposition always yield Schottky contact characteristics. The barrier height improvement at the n-GZO/p-InP interface is proposed using dual zinc driven-in steps and a NiO_x insertion layer to realize ohmic characteristics. The high zinc concentration (5-8 × 10¹⁸ cm^-3) is first obtained in the surface of the p-InP window layer via the dual zinc driven-in steps. By inserting a NiO_x layer between the GZO and Au/Cr contact films, the Au/Cr/GZO/NiO_x contact pad for zinc driven-in p-InP window layer and the postannealing process of 430 °C for 180 s exhibits a good ohmic contact behavior and a low specific contact resistance of 3.07 × 10^-4 Ωcm².

High-Speed and High-Light Output Power of InGaAs/GaAs HBLETs With an InMoO x Contact

A high-speed and high-light-output-power InGaAs/GaAs heterojunction bipolar light-emitting transistors (HBLETs) at 968-nm wavelength employing indium molybdenum oxide (IMO) contact are demonstrated in this letter. The IMO contact exhibits a low electrical resistivity of \(3.5 \times 10^{\mathrm {\mathbf {-4}}}~\Omega \) -cm accompanied with an extremely high optical transmittance of 99% at 968 nm, which can be ascribed to larger valence difference between In3+ matrix and Mo6+ dopants. As compared to HBLET with conventional AuGe contact, HBLET with IMO contact shows a higher forward voltage and higher series resistance. However, at the corresponding injection current level, HBLET with IMO contact produces a light output power with a rate of \(5.7~\mu \) W/mA, which is twice of \(2.7~\mu \) W/mA for HBLET with AuGe contact. In addition, HBLET with IMO contact exhibits a 3-dB optical bandwidth of 649 MHz, which is correlated to a carrier recombination lifetime of 245 ps. The successful incorporation of an IMO contact into an HBLET can improve the optical output extraction significantly without the expense of losing modulation speed.

Deposition of Transparent Indium Molybdenum Oxide Thin Films and the Application for Organic Solar Cells

In this study, we systematically investigate the effects of post-annealing on the structural, electrical, and optical characteristics of indium molybdenum oxide (IMO) films. The incorporation of IMO films into organic solar cells (OSCs) is further studied. The optimum content of Mo is 2.36 wt %. Furthermore, a significant improvement in crystallinity, surface morphology, electrical resistivity, and optical transmittance is observed after thermal annealing. The lowest resistivity is obtained with post annealing at 300 °C for 140 s. The OSC utilizing the IMO electrode shows an efficiency of up to 3.77%, which is higher than that of the OSC utilizing the ITO electrode. The diffusion length of the carriers in the OSC is approximately 10 nm. Thus, the higher efficiency can be explained by the smoother surface morphology of the post annealed IMO electrode. These results indicate that the novel IMO films with superior material properties have enormous potential applications for solar cells.

Effects of O2 plasma post-treatment on ZnO: Ga thin films grown by H2O-thermal ALD

Transparent conducting oxides have been widely employed in optoelectronic devices using the various deposition methods such as sputtering, thermal evaporator, and e-gun evaporator technologies.1-3 In this work, gallium doped zinc oxide (ZnO:Ga) thin films were grown on glass substrates via H2O-thermal atomic layer deposition (ALD) at different deposition temperatures. ALD-GZO thin films were constituted as a layer-by-layer structure by stacking zinc oxides and gallium oxides. Diethylzinc (DEZ), triethylgallium (TEG) and H2O were used as zinc, gallium precursors and oxygen source, respectively. Furthermore, we investigated the influences of O2 plasma post-treatment power on the surface morphology, electrical and optical property of ZnO:Ga films. As the result of O2 plasma post-treatment, the characteristics of ZnO:Ga films exhibit a smooth surface, low resistivity, high carrier concentration, and high optical transmittance in the visible spectrum. However, the transmittance decreases with O2 plasma power in the near- and mid-infrared regions.