C. K. Chia

Effects of AlAs interfacial layer on material and optical properties of GaAs∕Ge(100) epitaxy

GaAs∕AlAs∕Ge(100) samples grown at 650°C with AlAs interfacial layer thickness of 0, 10, 20, and 30nm were characterized using transmission electron microscopy, secondary ion mass spectrometry (SIMS), and photoluminescence (PL) techniques. SIMS results indicate that the presence of an ultrathin AlAs interfacial layer at the GaAs∕Ge interface has dramatically blocked the cross diffusion of Ge, Ga, and As atoms, attributed to the higher Al–As bonding energy. The optical quality of the GaAs epitaxy with a thin AlAs interfacial layer is found to be improved with complete elimination of PL originated from Ge-based complexes, in corroboration with SIMS results.

Interfacial characteristics and band alignments for ZrO2 gate dielectric on Si passivated p-GaAs substrate

The interfacial characteristics and band alignments of high-k ZrO2 on p-GaAs have been investigated by using x-ray photoelectron spectroscopy and electrical measurements. It has been demonstrated that the presence of Si interfacial passivation layer (IPL) improves GaAs metal-oxide-semiconductor device characteristics such as interface state density, accumulation capacitance, and hysteresis. It is also found that Si IPL can reduce interfacial GaAs-oxide formation and increases effective valence-band offset at ZrO2∕p-GaAs interface. The effective valence-band offsets of ZrO2∕p-GaAs and ZrO2∕Si∕p-GaAs interfaces are determined to be 2.7 and 2.84eV, while the effective conduction-band offsets are found to be 1.67 and 1.53eV, respectively.

Group-V intermixing in InAs∕InP quantum dots

Postgrowth intermixing in InAs∕InP quantum dot (QD) structures have been investigated by rapid thermal annealing and laser irradiation techniques. In both cases, room-temperature photoluminescence (PL) measured from the QD structures after intermixing shows a substantial blueshift accompanied by an improvement in PL intensity and a reduction in linewidth. In the case of impurity free vacancy disordering, an energy shift of up to 350meV has been achieved. The maximum differential energy shift for samples capped with SiO2 and SiNx dielectrics was found to be 90meV. On the other hand, laser-induced intermixing allows differential energy shifts of more than 250meV in this material system. Micro-Raman measurement shows the appearance of InAs-type and InP-type optical phonon peaks from laser-annealed InAs∕InP QDs due to the exchange of As and P at the QD interfaces.

Characterization of sputtered TiO2 gate dielectric on aluminum oxynitride passivated p-GaAs

Structural and electrical characteristics of sputtered TiO2 gate dielectric on p-GaAs substrates have been investigated. It has been demonstrated that the introduction of thin aluminum oxynitride (AlON) layer between TiO2 and p-GaAs improves the interface quality. X-ray photoelectron spectroscopy and transmission electron microscopy results show that the AlON layer effectively suppresses the interfacial oxide formation during thermal treatment. The effective dielectric constant value is 1.5 times higher for the TiO2∕AlON gate stack compared to directly deposited TiO2 on p-GaAs substrates, with a comparable interface state density. The capacitance-voltage (C-V), current-voltage (I-V) characteristics, and charge trapping behavior of the TiO2∕AlON gate stack under constant voltage stressing exhibit an excellent interface quality and high dielectric reliability, making the films suitable for GaAs based complementary metal-oxide-semiconductor technology.

HfOxNy gate dielectric on p-GaAs

Plasma nitridation method is used for nitrogen incorporation in HfO2 based gate dielectrics for future GaAs-based devices. The nitrided HfO2 (HfOxNy) films on p-GaAs improve metal-oxide-semiconductor device characteristics such as interface state density, accumulation capacitance, hysteresis, and leakage current. An equivalent oxide thickness of 3.6 nm and a leakage current density of 10−6 A cm−2 have been achieved at VFB−1 V for nitrided HfO2 films. A nitride interfacial layer (GaAsO:N) was observed at HfO2–GaAs interface, which can reduce the outdiffusion of elemental Ga and As during post-thermal annealing process. Such suppression of outdiffusion led to a substantial enhancement in the overall dielectric properties of the HfO2 film.

Ultrawide band quantum dot light emitting device by postfabrication laser annealing

An ultrawide band quantum dot (QD) light emitting device (LED) with bandwidth of 360nm covering 1284–1644nm spectral range has been demonstrated by postfabrication laser-irradiation technique. The integrated light output of the QD LED was found to increase by four times after laser annealing, attributed to the improved homogeneity of the QDs and enhanced lateral electrical and optical confinements at the active region after intermixing. Large wavelength blueshift of 315nm has been obtained at the laser annealed region and an overall increase in bandwidth of 22% has been obtained in the QD LED after postfabrication laser annealing.An ultrawide band quantum dot (QD) light emitting device (LED) with bandwidth of 360nm covering 1284–1644nm spectral range has been demonstrated by postfabrication laser-irradiation technique. The integrated light output of the QD LED was found to increase by four times after laser annealing, attributed to the improved homogeneity of the QDs and enhanced lateral electrical and optical confinements at the active region after intermixing. Large wavelength blueshift of 315nm has been obtained at the laser annealed region and an overall increase in bandwidth of 22% has been obtained in the QD LED after postfabrication laser annealing.

Atomic layer deposited (TiO2)x(Al2O3)1−x/In0.53Ga0.47As gate stacks for III-V based metal-oxide-semiconductor field-effect transistor applications

Atomic layer deposited (ALD) (TiO2)x(Al2O3)1-x(TiAlO) alloy gate dielectrics on In0.47Ga0.53As/InP substrates are shown to produce high quality interfaces between TiAlO and InGaAs. The surface morphology and interfacial reaction of nanolaminate ALD TiAlO on In0.53Ga0.47As are studied using atomic force microscopy and x-ray photoelectron spectroscopy. Measured valence and conduction band offsets are found to be 2.85 ± 0.05 and 1.25 ± 0.05 eV, respectively. Capacitance-voltage characteristics show low frequency dispersion (∼11%), interface state density (∼4.2 × 1011 cm−2eV−1), and hysteresis voltage (∼90 mV). Ga-O and As-O bonding are found to get suppressed in the gate stacks after post deposition annealing. Our experimental results suggest that higher oxidation states of In and Ga at the In0.53Ga0.47As surface and As diffusion in the dielectric are effectively controlled by Ti incorporation in Al2O3.

Role of AlxGa1−xAs buffer layer in heterogeneous integration of GaAs/Ge

The material and optical properties of the GaAs/AlxGa1−xAs/Ge structures grown by metalorganic chemical vapor deposition were examined and found to be dependent of the Al content x. SIMS and PL measurements show that the 10 nm AlxGa1−xAs buffer layer with x = 0.3 and 0.6 are equally effective in suppressing the outdiffusion of Ge, whereas x = 1.0 gives the most abrupt interface. The best morphology with surface rms of 0.3 nm is obtained in the structure with x = 0.3 buffer layer. Analysis on change of strain in the AlxGa1−xAs buffer layer suggests that the compressive strain at the AlxGa1−xAs-GaAs interface is compensated by the tensile strain at the Ge-AlxGa1−xAs interface when x ∼ 0.3. AlxGa1−xAs lattice matched to Ge is crucial for better result in surface morphology, but higher Al content is preferred for eliminating the interdiffusion of atoms at the heterointerface.

Interfacial and Electrical Characterization of Atomic-Layer-Deposited HfO2 Gate Dielectric on High Mobility Epitaxial GaAs/Ge Channel Substrates

Interfacial and electrical properties of atomic-layer-deposited HfO 2 gate dielectric on epitaxial GaAs (epi-GaAs)/Ge and bulk GaAs substrates have been investigated. Atomic layer deposition provides a unique opportunity to integrate high quality gate dielectrics on epi-GaAs. The cross-sectional transmission electron microscopy of a HfO 2 /III-V gate stack shows a similar interfacial layer thickness for HfO 2 on bulk p-GaAs and epi-GaAs substrates. However, X-ray photoelectron spectroscopy shows a Ga oxide-rich interfacial layer after postdeposition annealing at 500°C for films grown on epi-GaAs. Although the epi-GaAs surface is rough with nanoscale features, the electrical properties of the HfO 2 gate dielectric deposited on epi-GaAs are comparable with bulk p-GaAs-based devices. The Au/HfO 2 /epi-GaAs gate stack shows a low frequency dispersion (13%), hysteresis voltage (0.72 V), and a leakage current density of 2.1 X 10 ―3 A cm ―2 at V FB + 1 V (where FB is flatband) for an equivalent oxide thickness of 1.4 nm.

Impact of Buffer Layer on Atomic Layer Deposited TiAlO Alloy Dielectric Quality for Epitaxial-GaAs/Ge Device Application

The impact of AlGaAs and AlAs buffer layers on the electrical properties of an epitaxial gallium-arsenide (epi-GaAs) metal-oxide-semiconductor capacitor (MOSC) was investigated. MOSC was fabricated by using atomic-layer-deposited Al2O3 -TiO2 (TiAlO) alloy gate dielectric and epi-GaAs layers. The epi-GaAs layer was grown on Ge substrates at 675 °C with and without buffer layer between epi-GaAs layer and Ge substrates. The TiAlO/epi-GaAs interface with an AlGaAs buffer layer allows realizing a high-quality interface between epi-GaAs layers and TiAlO dielectric, much sought after for high-speed transistor applications on a silicon platform. TiAlO dielectric is amorphous even upon annealing at 500 °C and exhibits a sharp interface with epi-GaAs layers. The choice of AlGaAs over AlAs for a buffer layer was made based on the quality of resulting TiAlO/epi-GaAs surface passivation as evident through structural and electrical characteristics. Epi-GaAs with an AlGaAs buffer layer was found to improve the performance of the MOSC significantly through increase in accumulation capacitance and breakdown voltage. The interface state density, flatband voltage, frequency dispersion, and leakage current were decreased for the MOSC fabricated with an AlGaAs buffer layer.