Jay Curless

Field effect transistors with SrTiO3 gate dielectric on Si

SrTiO3 has been grown epitaxially by molecular beam epitaxy on Si. The capacitance of this 110 A dielectric film is electrically equivalent to less than 10 A of SiO2. This structure has been used to make capacitors and metal oxide semiconductor field effect transistors. The interface trap density between the SrTiO3 and the Si is 6.4×1010 states/cm2 eV and the inversion layer mobility is 221 and 62 cm2/V s for n- and p-channel devices, respectively. The gate leakage in these devices is two orders of magnitude smaller than a similar SiO2 gate dielectric field effect transistor.

Organic light-emitting diodes with a bipolar transport layer

A structure based on a bipolar transport/emitting layer is proposed and implemented for making organic light-emitting diodes. Compared to the conventional heterojunction organic light-emitting diodes, more than a factor of six improvement in device reliability (a projected operating lifetime of 70 000 h) is achieved in the structure. The significant improvement in device lifetime is attributed to the elimination of the heterointerface present in the conventional devices which greatly affects the device reliability.

Epitaxial oxide thin films on Si(001)

Over the years, the development of epitaxial oxides on silicon has been a great technological challenge. Amorphous silicon oxide layer forms quickly at the interface when the Si surface is exposed to oxygen, making the intended oxide heteroepitaxy on Si substrate extremely difficult. Epitaxial oxides such as BaTiO3 (BTO) and SrTiO3 (STO) integrated with Si are highly desirable for future generation transistor gate dielectric and ferroelectric memory cell applications. In this article, we review the recent progress in the heteroepitaxy of oxide thin films on Si(001) substrate by using the molecular beam epitaxy technique at Motorola Labs. Structural, interfacial and electrical properties of the oxide thin films on Si have been characterized using in situ reflection high energy electron diffraction, x-ray diffraction, spectroscopic ellipsometry, atomic force microscopy, Auger electron spectroscopy, x-ray photoelectron spectroscopy, high-resolution transmission electron microscopy, high-resolution transmissi...

Optical properties of bulk and thin-film SrTiO3 on Si and Pt

We have studied the optical properties (complex dielectric function) of bulk SrTiO3 and thin films on Si and Pt using spectroscopic ellipsometry over a very broad spectral range, starting at 0.03 eV [using Fourier transform infrared (FTIR) ellipsometry] to 8.7 eV. In the bulk crystals, we analyze the interband transitions in the spectra to determine the critical-point parameters. To interpret these transitions, we performed band structure calculations based on ab initio pseudopotentials within the local-density approximation. The dielectric function was also calculated within this framework and compared with our ellipsometry data. In the FTIR ellipsometry data, we notice a strong lattice absorption peak due to oxygen-related vibrations. Two longitudinal optic (LO) phonons were also identified. In SrTiO3 films on Si, the refractive index below the band gap decreases with decreasing thickness because of the increasing influence of the amorphous interfacial layer between the SrTiO3 film and the Si substrate....

Epitaxial perovskite thin films grown on silicon by molecular beam epitaxy

Thin film perovskite-type oxide SrTiO3 has been grown epitaxially on Si(001) substrate by molecular beam epitaxy. Reflection high energy electron diffraction and x-ray diffraction analysis indicate high quality SrTiO3 heteroepitaxy on Si substrate with SrTiO3(001)//Si(001) and SrTiO3[010]//Si[110]. The SrTiO3 surface is atomically as smooth as the starting substrate surface, with a root mean square roughness of 1.2 A observed by atomic force microscopy. The thickness of the amorphous interfacial layer between SrTiO3 and Si has been engineered to minimize the device short channel effect. An effective oxide thickness <10 A has been obtained for a 110 A thick dielectric film. The interface state density between SrTiO3 and Si is 6.4×1010 cm−2 eV−1, and the inversion layer carrier mobilities are 221 and 62 cm2 V−1 s−1 for n- and p-channel metal–oxide–semiconductor devices with 1.2 μm effective channel length, respectively. The gate leakage in these devices is two orders of magnitude smaller than a comparable S...

Development of integrated heterostructures on silicon by MBE

The semiconductor industry is facing the challenge of scaling of the gate dielectric of Si CMOS devices, which are continually being made smaller. Presently SiO/sub 2/ is being used, but at thickness below 20/spl Aring/, it suffers from high tunneling leakage current and reliability problems. Alternative high-k materials to replace SiO/sub 2/ need to be developed as soon as possible. The alkaline earth oxides such as barium strontium titanate (Ba/sub x/Sr/sub 1-x/TiO/sub 3/) have a substantially higher dielectric constant and are ideal candidates for gate dielectrics. Because of the higher dielectric constant a physically thicker layer can yield an equivalent oxide thickness of <20/spl Aring/, thereby eliminating the leakage problems experienced with ultra-thin SiO/sub 2/. These oxides also exhibit ferroelectric behavior and their use as the gate dielectric on Si can be exploited in the realization of a single transistor memory element. These types of oxides also have a number of functionalities which when combined with other types of semiconductors will enable the development of novel device applications. Molecular beam epitaxy can be used for the deposition of oxide based epitaxial layers both for Si device applications and integration of GaAs devices with silicon. The potential for increased functionality and integration of devices based on III-V semiconductors, crystalline oxides and silicon make this an attractive and promising technology.

Bipolar transport organic light emitting diodes with enhanced reliability by LiF doping

An electrode contact scheme based on the use of an organic LiF alloy is investigated. The performance of organic light emitting diodes (OLED) with this contact scheme in both heterojunction and bipolar transport/emitting layer (BTEL) OLED structures are compared with their counterparts with LiF buffer layers. The organic LiF contact scheme improved device reliability of BTEL OLEDs by 32% to 92 500 h while adversely affecting device reliability of heterojunction OLEDs.

Effects of substrate misorientation on the properties of (Al, Ga)As grown by molecular beam epitaxy

(Al,Ga)As layers have rough surface morphologies when deposited under certain growth conditions in molecular beam epitaxy (MBE). This leads to poor interfaces between GaAs and (Al,Ga)As and degraded performance in heterojunction devices. We have observed that by misorienting the substrate slightly from (100), in a manner specific to the growth conditions, smooth (Al,Ga)As layers can be grown at 675 °C for an Al mole fraction of 0.15. Similar conditions for nominal (100) result in a rough, textured morphology. The results suggest that the roughness is due to an energetic instability at the growth surface with respect to the formation of features such as terraces and hillocks. To our knowledge, this is the first reported experimental verification of singular instabilities in (Al,Ga)As grown by MBE. Smooth layers obtained by using an optimal misorientation of 2° 45’ from (100) towards (111)A also exhibit superior optical properties as determined from low‐temperature photoluminescence measurements. These find...

Development of high dielectric constant epitaxial oxides on silicon by molecular beam epitaxy

Thin films of perovskite-type oxide SrTiO 3 have been grown epitaxially on Si(001) substrates using molecular beam epitaxy. Using reflection high energy electron diffraction (RHEED) we have determined the optimum growth conditions for these type of oxides directly on silicon. Also, observations of RHEED during growth and X-ray diffraction (XRD) analysis indicate that high quality heteroepitaxy on Si takes place with SrTiO 3 (001)//Si(001) and SrTiO 3 [010]//Si[110]. Thin SrTiO 3 layers grown directly on Si were used as the gate dielectric for the fabrication of MOSFET devices. An effective oxide thickness < 10 A has been obtained for a 110 A thick SrTiO 3 dielectric film with interface state density around 6.4 x 10 10 cm -2 eV -1 , and the inversion layer carrier mobilities of 220 and 62 cm 2 V -1 s -1 for NMOS and PMOS devices, respectively.

Properties of AlxGa1−xAs (xAl≂0.3) grown by molecular‐beam epitaxy on misoriented substrates

The effects of substrate misorientation on the morphological and optical properties of AlxGa1−xAs (xAl≂0.3) grown by molecular‐beam epitaxy (MBE) have been studied. The substrate temperatures and V/III beam‐flux ratios used were such that layers grown on nominally (100) substrates typically exhibited rough morphologies and poor 4.2 K PL characteristics. By intentionally misorienting the substrate slightly from (100), smooth layers can be grown at 620 and 650 °C at typical MBE growth rates (≂1 μm/h). These smooth layers also exhibited sharp, exciton‐related emission peaks at 4.2 K with half‐widths as narrow as 5 meV. Since rough surfaces may lead to poor interfaces between GaAs and (Al,Ga)As and in turn to degraded performance in heterojunction devices, the present results may have significant implications for the performance of such structures grown by MBE.