Transparent oxide semiconductors for advanced display applications

The article discusses the progress and issues related to transparent oxide semiconductor (TOS) TFTs for advanced display and imaging applications. Amorphous oxide semiconductors continue to spark new technological developments in transparent electronics on a multitude of non-conventional substrates. Applications range from high-frame-rate interactive displays with embedded imaging to flexible electronics, where speed and transparency are essential requirements. TOS TFTs exhibit high transparency as well as high electron mobility even when fabricated at room temperature. Compared to conventional a-Si TFT technology, TOS TFTs have higher mobility and sufficiently good uniformity over large areas, similar in many ways to LTPS TFTs. Moreover, because the amorphous oxide semiconductor has higher mobility compared to that of conventional a-Si TFT technology, this allows higher-frame-rate display operation. This would greatly benefit OLED displays in particular because of the need for lower-cost higher-mobility analog circuits at every subpixel.

Challenges in visible wavelength detection using optically transparent oxide semiconductors

We discuss the development of amorphous oxide semiconductor technology for optical sensor applications. In particular, we discuss the challenges of detecting visible wavelengths using this family of materials, which are known to be optically transparent due to their relatively large bandgap energy. One of the main issues with amorphous oxide semiconductors (AOS) is the ionization of the oxygen vacancies (VO) under illumination. While this can be beneficial in terms of optical absorption and high photoconductive gain, it can give rise to persistent photoconductivity (PPC). We will present techniques to overcome the PPC, and discuss how to achieve the high photoconductive gain for image sensor applications. © 2012 IEEE.

III-V compound semiconductor nanowires for optoelectronic device applications

GaAs and InP based III-V compound semiconductor nanowires were grown epitaxially on GaAs (or Si) (111)B and InP (111)B substrates, respectively, by metalorganic chemical vapor deposition using Au nanoparticles as catalyst. In this paper, we will give an overview of nanowire research activities in our group. In particular, the effects of growth parameters on the crystal structure and optical properties of various nanowires were studied in detail. We have successfully obtained defect-free GaAs nanowires with nearly intrinsic exciton lifetime and vertical straight nanowires on Si (111)B substrates. The crystal structure of InP nanowires, i.e., WZ or ZB, can also be engineered by carefully controlling the V/III ratio and catalyst size. © 2011 World Scientific Publishing Company.

III-V compound semiconductor nanowires

InP and GaAs based nanowires were grown epitaxially on InP or GaAs (111)B substrates by metalorganic chemical vapor deposition via vapor-liquid-solid (VLS) mechanism. In this report, I will give an overview of nanowire research activities in our group. In particular, the effects of growth parameters for InP and GaAs nanowires on the crystal quality have been studied in detail. We demonstrated the ability to obtain defect-free GaAs nanowires and control the crystal structure of InP nanowires, ie, WZ or ZB, by choosing a combination of growth parameters, such as temperature, V/III ratio and nanowire diameter. © 2009 IEEE NANO Organizers.

III-V compound semiconductor nanowires

GaAs and InP based nanowires were grown epitaxially on GaAs or InP (111)B substrates by metalorganic chemical vapor deposition using Au nanoparticles as catalyst. In this talk, I will give an overview of nanowire research activities in our group. Especially, the effects of growth parameters for GaAs and InP nanowires on the crystal quality have been studied in detail. We demonstrated the ability to obtain defect-free GaAs nanowires and control the crystal structure of InP nanowires, ie, WZ or ZB, by choosing a combination of growth parameters, such as temperature, V/III ratio and nanowire diameter. © 2009 IEEE.

Light induced instability mechanism in amorphous InGaZn oxide semiconductors

A model of the negative bias illumination stress instability in InGaZn oxide is presented, based on the photo-excitation of electrons from oxygen interstitials. The O interstitials are present to compensate hydrogen donors. The O interstitials are found to spontaneously form in O-rich conditions for Fermi energies at the conduction band edge, much more easily that in related oxides. The excited electrons give rise to a persistent photoconductivity due to an energy barrier to recombination. The formation energy of the O interstitials varies with their separation from the H donors, which leads to a voltage stress dependence on the compensation. © 2014 AIP Publishing LLC.

Proposal for the direct optical detection of pure spin currents in semiconductors

We suggest a different practical scheme for the direct detection of pure spin current by using the two-color Faraday rotation of optical quantum interference process (QUIP) in a semiconductor system. We demonstrate theoretically that the Faraday rotation of QUIP depends sensitively on the spin orientation and wave vector of the carriers, and can be tuned by the relative phase and the polarization direction of the omega and 2 omega laser beams. By adjusting these parameters, the magnitude and direction of the spin current can be detected.

Effects of coupling lens on optical refrigeration of semiconductors

Optical refrigeration of semiconductors is encountering efficiency difficulties caused by nonradiative recombination and luminescence trapping. A commonly used approach for enhancing luminescence efficiency of a semiconductor device is coupling a lens with the device. We quantitatively study the effects of a coupling lens on optical refrigeration based on rate equations and photon recycling, and calculated cooling efficiencies of different coupling mechanisms and of different lens materials. A GaAs/GaInP heterostructure coupled with a homo-epitaxial GaInP hemispherical lens is recommended.