Ting-Ting Kang

Determination of the valence band offset of wurtzite InN∕ZnO heterojunction by x-ray photoelectron spectroscopy

The valence band offset (VBO) of the wurtzite InN/ZnO heterojunction is directly determined by x-ray photoelectron spectroscopy to be 0.82 +/- 0.23 eV. The conduction band offset is deduced from the known VBO value to be 1.85 -/+ 0.23 eV, which indicates a type-I band alignment for InN/ZnO heterojunction

Effect of gas flow on the growth of In-rich AlInN films by metal-organic chemical vapor deposition

Indium-rich AlInN are grown by metal-organic (MO) chemical vapor deposition using trimethylaluminum, trimethylindium, and ammonia. Under the conservation of MO influx, the effects of gas flow in the MO route on AlInN growth and Al-related parasitic reaction are investigated. With an increase in this gas flow, the suppression of Al-related parasitic reaction, i.e., enhancement in Al content incorporation and improvement of crystalline quality, is satisfactorily shown until the occurring of severe phase separation. Accordingly, Al content x in Al x In 1 − x N can be tuned from x = 0.02 to 0.26. The Raman spectra of those AlInN samples with phase separation are analyzed by the resonant excitation effect and two-mode behavior for A 1 ( LO ) . Finally, we propose a phase diagram to interpret the phase separation and Al content evolution under the influence of gas flow.

Terahertz characterization of semiconductor alloy AlInN: negative imaginary conductivity and its meaning

Through terahertz time-domain spectroscopy, negative imaginary conductivity is observed in In-rich AlInN film grown by metal-organic chemical-vapor deposition for frequencies from 0.2 to 2.0 THz. This non-Drude behavior is explained based on the electron back-scattering theory of Smith [Phys. Rev. B65, 115206 (2002)]. Comparing with binary semiconductor InN, potential fluctuations produced by composition inhomogeneity and alloy scattering of carriers make In-rich AlInN alloy easier to be subjected to non-Drude behavior in electrical performance.

Optical properties of InN containing metallic indium

We theoretically study the optical properties of the composite made of indium nitride (InN) containing metallic indium clusters, using quasistatic approximation and effective medium approximation. The influences of indium cluster shape and volume concentration on the optical properties of entire sample are systematically discussed. Our results can satisfactorily explain recent experiments on the dielectric function of InN containing indium [M. Losurdo, G. Bruno, T.-H. Kim, S. Choi, and A. Brown, Appl. Phys. Lett. 88, 121928 (2006)].

Using different carrier gases to control AlN film stress and the effect on morphology, structural properties and optical properties

On the metalorganic chemical vapour deposition growth of AlN, by adjusting H-2+N-2 mixture gas components, we can gradually control island dimension. During the Volmer - Weber growth, the 2-dimensional coalescence of the islands induces an intrinsic tensile stress. Then, this process can control the in-plane stress: with the N-2 content increasing from 0 to 3 slm, the in-plane stress gradually changes from 1.5 GPa tensile stress to - 1.2GPa compressive stress. Especially, with the 0.5 slm N-2 + 2.5 slm H-2 mixture gas, the in-plane stress is only 0.1 GPa, which is close to the complete relaxation state. Under this condition, this sample has good crystal and optical qualities.

Photoconductivity of InN grown by MOVPE: Low temperature and weak light illumination

Using a light-emitting diode instead of a laser, we study the photoconductivity (PC) in the metalorganic vapor phase epitaxy grown InN films under 2.3 K–280 K temperature with blocked 300 K blackbody radiation. Although InNs negative PC was observed, it shows a quick response, not a “persistent” one as previously described by PC measurements using laser. An artificial “persistent negative PC” has been experimentally demonstrated by the light heating effect (LHE). The quick response negative PC is weakened by increased temperature and is less dependent on the light intensity. Further analyses show that the so-called “persistent photoconductivity” in InN might be justified as LHE.

Highly photoresponsive charge-sensitive infrared phototransistors with a dynamically controlled optical gate

Charge-sensitive infrared phototransistors (CSIPs) with a built-in field-effect-induced amplification mechanism have much higher infrared photoresponsivity ( ≥103 A/W) than conventional detectors, which is often restricted by background black-body radiation induced saturation. Here, we report that dynamically controlling the electrostatic potential of the photosensitive floating gate of a CSIP can counterbalance this background-induced saturation effect. As a result, the CSIP photoresponsivity can be improved by about one order of magnitude, reaching as high as ∼1.2×104 A/W to external blinking light. Our work suggests that time-domain manipulation could be an agile degree of freedom in optimizing the CSIP performance and provide insight into operating more general phototransistors for a wide variety of optoelectronic applications.

An Anomalous Conductance Decrease in Charge Sensitive Infrared Phototransistor

For charge-sensitive infrared phototransistors (CSIP), it is observed that “conductance decrease,” which is contrary to the standard “conductance increase” photon response, can also happen after absorbing infrared light. By experimental modeling the charge-up detection mechanism of CSIP via a capacitive way, we clarify that “conductance decrease” should be attributed to the significantly reduced low quantum well electron mobility after the photon-charging process, rather than a reversed electron transfer. This experimental result clearly indicates that photon-induced charges are able to modify the electron mobility in those “charge-sensitive sensor” types of semiconductor quantum single-photon detectors.

Terahertz characterization of semiconductor alloy AlInN: negative imaginary conductivity and its meaning: reply to comment

Through terahertz time-domain spectroscopy, negative imaginary conductivity is observed in In-rich AlInN film grown by metal-organic chemical-vapor deposition for frequencies from 0.2 to 2.0 THz. This non-Drude behavior is explained based on the electron back-scattering theory of Smith [Phys. Rev. B65, 115206 (2002)]. Comparing with binary semiconductor InN, potential fluctuations produced by composition inhomogeneity and alloy scattering of carriers make In-rich AlInN alloy easier to be subjected to non-Drude behavior in electrical performance.

Some Failure Mechanisms in Charge-Sensitive Infrared Phototransistors

For an infrared photon detector, such as charge-sensitive infrared phototransistors (CSIPs), we propose and use a capacitive charging method to study some failure mechanisms that disable the photon response of CSIPs. Two failure mechanisms are highlighted, namely interquantum well (QW) leakage and low tunneling probability for intersubband-transition-excited electrons. A correlation between the Al content in the inter-QW AlGaAs barrier and the failure mechanism type are discussed. On the other hand, the previously unexplained puzzle that the success of photon response is only weakly dependent on the QW electron mobility that is attributed to an imperfect inter-QW barrier.