Complex oxides and semiconductors exhibit distinct yet complementary propertiesowing to their respective ionic and covalent natures. By electrically couplingoxides to semiconductors within epitaxial heterostructures, enhanced or novelfunctionalities beyond those of the constituent materials can potentially berealized. Key to electrically coupling oxides to semiconductors is controllingthe physical and electronic structure of semiconductor – crystallineoxide heterostructures. Here we discuss how composition of the oxide can bemanipulated to control physical and electronic structure inBa1-xSrxTiO3/ Ge andSrZrxTi1-xO3/Ge heterostructures. In thecase of the former we discuss how strain can be engineered through compositionto enable the re-orientable ferroelectric polarization to be coupled to carriersin the semiconductor. In the case of the latter we discuss how composition canbe exploited to control the band offset at the semiconductor - oxide interface.The ability to control the band offset, i.e. band-gap engineering, provides apathway to electrically couple crystalline oxides to semiconductors to realize ahost of functionalities.

Thin-film transistors (TFT) were fabricated at a room-temperature (RT) with zincoxide (ZnO) channel and indium molybdenum oxide (IMO) electrodes. To isolate thegate oxide and gate electrode influence on the device performance, common gateconfiguration on a commercial substrate with thermal SiO2 (100 nm)was selected. A threshold voltage (V Th) of 10 V and I ON/I OFF ratio of 1 × 10-5 were obtained. Once the referencedata was taken transistors were exposed to glycerol. Temporary changes in devicecharacteristics were observed due to the influence of glycerol, a lowconductivity medium. To exclude the possibility of sugar alcohol being the mainconductor, measurement on dummy transistor electrode was performed retaining thedistance between probes. The TFT device under test revealed ten times higherdrain current but also a change in threshold voltage and leakage current.Transistors under glycerol influence were always open with the positive gatebias.

For exploring the prospect of higher-k dielectric phase engineering on a highmobility substrate, films of Hf1-xZrxO2 withvarying x-values (0 ≤ x ≤ 1) were deposited onAl2O3 passivated Ge substrates using atomic layerdeposition (ALD) with a cyclic deposit-anneal-deposit-anneal (DADA) scheme. Theevolution of monoclinic to higher-k tetragonal structure with increasingZrO2 concentration was probed by grazing incident x-raydiffraction and partial reciprocal space maps using the highly brilliantsynchrotron x-ray source at the Cornell High Energy Synchrotron Source (CHESS).A primarily amorphous/nano-crystalline matrix of the asdeposited films changedto randomly aligned grains of nanocrystalline MO2 (M=Hf, Zr)after post deposition annealing at 800 °C for 200 seconds. In contrast,the DADA films annealed for same thermal budget showed high degree of preferredorientation along certain crystallographic directions. With increasingZrO2 content, the structure of the films changed from a monoclinic toa tetragonal phase. A lower amount of ZrO2 (x = 0.33) wasrequired for stabilizing the tetragonal phase in films grown onAl2O3 passivated Ge substrate as compared to similarfilms grown on a Si substrate via the same DADA process (x ≥0.50).

Ferroelectric materials such as BaTiO3 have been studied for emergingnon-volatile memory applications. However, most of the previous work has beenfocused on this material when it was deposited on insulting oxide substratessuch as SrTiO3. Unfortunately, this substrate is not suitable forCMOS-based microelectronics applications. This motivated us to carry out thepresent work. We have studied the resistive switching behavior inBaTiO3/La0.7Sr0.3MnO3 (BTO/LSMO)heterostructures integrated with semiconducting substrates Si (100) usingMgO/TiN buffer layers by pulsed laser deposition. Current-Voltage (I-V)measurements were conducted on BTO (500nm)/LSMO (25nm) devices at 200K. We haveobserved a broad hysteresis in forward and reverse voltage sweeps which is animportant property for memory applications. Secondly, theRON/ROFF ratio is estimated at ∼ 150,consistent with the reported numbers (30-100) in the literature. Thirdly, thedevice is stable at least up to 50 cycles. However, we found that hystereticbehavior was suppressed upon oxygen annealing of the device at 1 atmosphericpressure, 200° C for 1hr, inferring the important role ofoxygen vacancies in the resistive switching behavior of BTO/LSMO device. Futurework will focus on investigating the correlation between ferroelectricity andresistive switching in these devices using local probe technique piezo forcemicroscopy (PFM) technique.

Thin-film transistors (TFT) were fabricated at room-temperature (RT) utilizingzinc oxide (ZnO) channel and indium molybdenum oxide (IMO) electrodes. Thecommon bottom-gate TFTs were fabricated on commercially available thermalsilicon oxide (100 nm thick) coated silicon wafers. A total of 100 devices weremade in a 1 inch square area as 10 × 10 matrix, by varying the channelwidth and length, between 5 µm and 300 µm. Output and transfercharacteristics of the fabricated devices were extracted from a semiconductorparameter analyzer. A threshold voltage (V Th) of 10 V and an I ON/I OFF ratio of 1 × 10-5 were obtained. The impact ofchannel dimensions on the device performance was investigated, confirming thatthe saturation current (I sat) is directly proportional to the channel width (W), andinversely proportional to channel length (L), in agreement withfield effect device theory.

Integrating oxide heterostructures on silicon has the potential to leverage themultifunctionalities of oxide systems into semiconductor device technology. Wepresent the growth and characterization of two-dimensional electron gas (2DEG)oxide systems LaTiO3/SrTiO3 (LTO/STO) andGdTiO3/SrTiO3 (GTO/STO) on Si(001). We showinterface-based conductivity in the oxide films and measure high electrondensities ranging from ∼9 × 1013 cm-2interface-1 in GTO/STO/Si to ∼9 ×1014 cm-2 interface-1 in LTO/STO/Si. Weattribute the higher measured carrier density in the LTO/STO films to a higherconcentration of interface-bound oxygen vacancies arising from a lower oxygenpartial pressure during growth. These vacancies donate conduction electrons andresult in an increased measured carrier density. The integration of such 2DEGoxide systems with silicon provides a bridge between the diverse electronicproperties of oxide systems and the established semiconductor platform andpoints toward new devices and functionalities.

The present work accentuates the effect of UV laser irradiation on theconductivity of nickel oxide (NiO) thin films, deposited at various temperaturesby radio-frequency reactive sputtering of Ni in oxygen containing atmosphere.The effect of UV irradiation on zinc oxide – nickel oxideheterostructures, obtained by sputtering, was examined as well. It was foundthat the resistivity of NiO changes from 12 Ω-cm to 0.62Ω-cm, and the majority carrier concentration from3.95x1017 holes/cm3 to 4.22x1020electrons/cm3. The current-voltage (I-V) characteristics of theZnO/NiO heterostructure shows an improved p-n diode behavior with the forwardbias current increasing for the laser-irradiated ZnO/NiO compared to theas-deposited stack. The observed improvement in diode-like behavior suggeststhat laser irradiation can be an important technique to controllably change thestructural, electrical and optical properties of metal oxide thin films.

Pulsed metal organic chemical vapor deposition (PMOCVD) was used to grow high Mgcontent, high quality, wurtzite MgxZn1-xO (MgZnO)epitaxial film to realize photodetectors and emitters in the solar blindspectral window. MgZnO films with various Mg contents were deposited on c-planeAl2O3 with and without AlN buffer layer. The band gapof the films range from 3.24 eV to 4.49 eV, corresponding to fraction of Mgbetween x=0.0 to x=0.51, asdetermined by Rutherford backscattering spectroscopy (RBS). Cathodoluminescence(CL) measurement showed a linear blue shift in the spectral peak position ofMgxZn1-xO with an increase in x. Nomulti-absorption edge or CL band splitting was observed, indicating the phasepurity of the films and was confirmed by XRD analysis. The surface quality ofthe films has improved with the increase in Mg content. To the best of ourknowledge, the current result shows the highest Mg content(x=0.51), high quality, single phase wurtzite MgZnOepitaxial film ever grown by MOCVD. This is realized due to the non-equilibriumbehavior of PMOCVD in which radicals that are formed during the growth processwill have insufficient time to reach equilibrium.

All inorganic quantum dot light emitting devices with solution processedtransport layers are investigated. The device consists of an anode, a holetransport layer, a quantum dot emissive layer, an electron transport layer and acathode. Indium tin oxide coated glass slides are used as substrates with theindium tin oxide acting as the transparent anode electrode. The transport layersare both inorganic, which are relatively insensitive to moisture and otherenvironmental factors as compared to their organic counterparts. Nickel oxideacts as the hole transport layer, while zinc oxide nanocrystals act as theelectron transport layer. The nickel oxide hole transport layer is formed byannealing a spin coated layer of nickel hydroxide sol-gel. On top of the holetransport layer, CdSe/ZnS quantum dots synthesized by hot injection method isspin coated. Finally, zinc oxide nanocrystals, dispersed in methanol, are spincoated over the quantum dot emissive layer as the electron transport layer. Thematerial characterization of different layers is performed by using absorbance,Raman scattering, XRD, and photoluminescence measurements. The completed deviceperformance is evaluated by measuring the IV characteristics,electroluminescence and quantum efficiency measurements. The device turn on isaround 4V with a maximum current density of ∼200 mA/cm2 at9 V.

In this paper, we will report on the formation of HfSixOylayer on an HF-last Si(100) substrate by atomic layer deposition fromtetrakis(dimethylamido)hafnium (TDMAH) and atomic oxygen generated by amicrowave remote plasma. Transmission electron microscopy observations ofHfSixOy /Si structures deposited at 100 and300℃ revealed that 3∼5-nm-thick amorphousHfSixOy layers were unintentionally formed precededthe growth of crystalline Hf-rich HfSixOy layers. Tounderstand the mechanism of this unintentional growth ofHfSixOy, the depth profiles of Hf, O and Si elements weremeasured by X-ray photoelectron spectroscopy. It was found that Hf atoms deeplydiffused into the Si substrate. From these results, suppression of Hf indiffusion to the Si substrate must be important to reduce the capacitanceequivalent thickness of the metal-oxide-semiconductor capacitors. The roles ofTDMAH and plasma-generated oxygen radical on the enhanced diffusion of Hf willbe discussed in detail.