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In this work, we fabricated vertical organic thin film transistors (VOTFTs) with lead phthalocyanine (PbPc) as the active layer and analyzed the operating characteristics and current transfer mechanism of VOTFTs. The results show that the quiescent output current of VOTFTs is not saturated, and the output current can be modulated by requiring different gate voltages. The switching parameters of the VOTFTs are ton = 2.5 μs, toff = 3.5μs, and the switching characteristic time reaches the microsecond level. When a sine wave dynamic signal is applied to the gate electrode, the cut-off frequency fc = 77 kHz. The experimental results demonstrate that short channel and vertical structure of VOTFTs make up for organic semiconductor material defects of low carrier mobility and realize high speed and low driving voltage of organic devices. Electric field intensity of depletion layer in the gate region is 7×107V/m, and high electric field intensity makes carriers tunneling become the major transport mode. The tunnel injection model is used to analyze the carrier transport inside the transistor. The results show that the operating current of the transistor conforms to the tunneling effect theory.

A tunnelling effect transistor based on copper phthalocyanine (CuPc) has been fabricated. CuPc is the active layer of transistors. The basic characteristics of the transistor are measured. The device shows unsaturated output characteristics. The output current can be modulated by demanding different gate voltage. At V DS = 3 V and V GS = 0 V, the drain-source current is 1.89 × 10−4 A. The current density is 4.73 × 10−3 A/cm2. The tunnel injection model is used to analyse the carrier transport inside the transistor. The microscopic operating mechanism of the device is investigated. The results show that the operating current of the transistor conforms to the tunnelling effect theory.

Transistor Laser has already established as a promising candidate for high speed optical interconnects and optical telecommunication networks. The present work is focused on the performance of multiple quantum wells (MQW) based transistor laser by incorporating tunnel injection phenomenon and it’s performance by varying the width of the separate confinement heterostructure layer. The virtual state (VS) is assumed as a path for the movement of injected charge carriers from bulk to nanostructures. We have estimated the various characteristics such as base threshold current, light power output, and optical modulation response by considering various physical parameters such as diffusion time, gain compression factor, optical confinement factor, photon lifetime, tunneling time and diffusion length, as a function of separate confinement hetero-structure (SCH) layer thickness. It is found that with increasing thickness of the SCH layer, base threshold current reduces, the light output power increases, but the optical modulation response remains almost constant, which ensures the potentiality of the proposed structure for high speed opto-electronic transmitter with low power consumption.

An InP based tunnel injection quantum dot (QD) laser and a reference quantum dot laser designed to emit at 1.55 μ m were grown by molecular beam epitaxy. The lattice matched tunnel injection (TI) structures consist of an InGaAs quantum well (QW), an InAlGaAs barrier and multiple InAs quantum dot layers. Quantum well and quantum dot test structures as well as the actual laser structures were treated with rapid thermal annealing (RTA) at varying temperatures (680–780 °C). Photoluminescence measurements were performed at 10 K on all samples and a strong effect of this annealing process on the emission properties is observed. The laser structures were processed into broad area lasers. Power-current characteristics were measured and evaluated. A strong improvement in device performance is observed after annealing for QD lasers while for TI-QD lasers no significant improvement was obtained, which might be caused by detuning of band energy alignment and different impact of the RTA process on the material quality of QW and QD layers.

We studied the hysteresis and electric field effects on planar CH3NH3PbI3 perovskite devices, synthetized from laser-ablated precursors, by means of electrical characterizations at different scan rates and optical measurements. The aim of our investigation is to characterize the phenomena behind perovskite degradation under prolonged applied electric field. Using a perovskite more resistant to electric field induced degradation, we run long time characterizations that were not accomplishable before. Thus, we distinguished all the degradation-involved phenomena. The results point to the presence of ions migrating in the perovskite when the device is biased. Our data showed that ion migration degrades the interfaces with the consequent creation of degradation layers that limit the current injected in the device and the extracted photocurrent. These layers where detected also by means of optical Raman characterization. In order to explain the details of the mechanisms concurring to the observed behaviors, we presented a qualitative model. The observed phenomena exacerbated by the planar structure are even more destructive on standard solution processed perovskites to which the results of this work can be extended. Since, the same degradation dynamics occur on vertical devices, typical on perovskite solar cells, this work provides a useful in-depth analysis of the ionic migration effects.

Charge accumulation in metal—oxide—semiconductor (MOS) structures with a doped and undoped polysilicon gate with Al contacts and without them under tunnel electron injection from the gate and silicon substrate is investigated. It is shown that negative charge is accumulated near the polysilicon gate irrespective of the injection polarity, and positive charge is accumulated near the silicon substrate. Negative charge also appears near the silicon substrate at large injection charges. The results are described with the help of a numerical model, in which the formation of electron traps with the deposition of Al contacts and the generation of electron traps during the recombination of free electrons with holes captured at traps is taken into account.

The paper suggests a design of radiation sensors based on metal-oxide-semiconductor (MOS) structures and p-channel radiation sensitive field effect transistors (RADFET) which are capable to function under conditions of high-field tunnel injection of electrons into the dielectric. We demonstrate that under these conditions, the dose sensitivity of the sensor can be significantly raised, and, besides, the intensity of radiation can be monitored in situ on the basis of determining the ionization current arising in the dielectric film. The paper proposes the model allowing to make a quantitative analysis of charge effects taking place in the radiation MOS sensors under concurrent influence of ionization radiation and high-field tunnel injection of electrons. Use of the model allows to properly interpret results of the radiation control. In order to test the designed sensors experimentally, we have utilized &gamma, rays, &alpha, particle radiation, and proton beams. We have acquired experimental results verifying the enhancement of function capabilities of the radiation MOS sensors when these have been under high-field injection of electrons into the dielectric.

In this paper, for the first time, the switchable two-color quantum dot laser has been realized considering solution process technology, which has both simultaneous and lonely lasing capability exploiting selective energy contacts. Furthermore, both channels can be modulated independently, which is a significant feature in high-speed data transmission. To this end, utilizing superimposed quantum dots with various radii in the active layer provides the different emission wavelengths. In order to achieve the different sizes of QDs, solution process technology has been used as a cost-effectiveness and fabrication ease method. Moreover, at the introduced structure to accomplish the idea, the quantum wells are used as separate selective energy contacts to control the lasing channels at the desired wavelength. It makes the prominent device have simultaneous lasing at different emission wavelengths or be able to lase just at one wavelength. The performance of the proposed device has been modeled based on developed rate equation by assuming inhomogeneous broadening of energy levels as a consequence of the size distribution of quantum dots and considering tunnel injection of carriers into the quantum dots via selective energy contacts. Based on simulation results, the simultaneous lasing in both or at one of two wavelengths 1.31 μm and 1.55 μm has been realized by the superimposition of two different sizes of InGaAs quantum dots in a single cavity and accomplishment of selective energy contacts. Besides, controlling the quantum dot coverage leads to managing the output power and modulation response at the desired wavelengths. By offering this idea, one more step is actually taken to approach the switchable QD-laser by the simple solution process method.

Monolithic integration of a laser diode with a modulator usually requires complicated and potentially defect-generating processing steps such as epitaxial regrowth or bonding. Alternatively, the same medium grown in a single epitaxial run can be used in both gain and electro-absorption section. We demonstrate a universal active medium with tunnel coupled InGaAs short period superlattice (SPSL) quantum well grown on InAs quantum dots (QW-on-QDs) in an AlGaAs waveguide. In this configuration, the QW serves as a tunnel injector of electrons into the QDs in the forward-biased gain section, while in the reverse-biased modulator section the InGaAs QW acts as a wavelength matched quantum Stark effect electro-absorber. The optimum QW and QD ground state separation is close to 30meV for efficient tunnel injection into QDs to increase the gain. The 3x(QW-on-QDs) double heterostructure with separate 0.3μm waveguide was grown by molecular beam epitaxy on n-type GaAs substrate. The device was processed into two-section dies with an intermediate distributed Bragg reflector (DBR) between the sections. Focused ion beam air-gap DBR fabrication with low electrical leakage and required (~30%) optical mode reflection was employed. The laser-modulator performance with slope efficiency over 50%, 6dB power modulation, linear dynamic range>24dB at 2GHz was shown with a 200μm long modulator section and low optical feedback from the modulator to laser.

The small and large signal responses of InP-based 1.55 μm high-speed quantum dot (QD) lasers with and without tunnel-injection (TI) quantum well (QW) and/or p-type doping in the active region (incorporating nominally identical QDs) were designed, manufactured and compared. The structures were grown by a molecular beam epitaxy system equipped with group-V valved cracker cells. In all cases, the active region consisted of six QD or TI-QD structures, which were embedded in InAlGaAs barriers lattice matched to InP. The InGaAs TI-QWs were separated by a thin InAlGaAs tunnel barrier from the InAs QDs. The laser structures were processed into ridge waveguide lasers and analyzed. The results show, that the bandwidth and maximum data rates were reduced by incorporation of TI-QWs. P-doping resulted in slightly worse performance of the simple QD laser, but in an improvement of the TI QD laser. Furthermore, the large signal response of the tunneling injection QD laser is one of the first reports of digital modulation of such a laser. An optimization of the doping profile is promising to further improve the laser performance over the undoped counterparts.

InP based lattice matched tunnel injection structures consisting of a InGaAs quantum well, InAlGaAs barrier and InAs quantum dots designed to emit at 1.55 μ m were grown by molecular beam epitaxy and investigated by photoluminescence spectroscopy and atomic force microscopy. The strong influence of quantum well and barrier thicknesses on the samples emission properties at low and room temperatures was investigated. The phenomenon of a decreased photoluminescence linewidth of tunnel injection structures compared to a reference InAs quantum dots sample could be explained by the selection of the emitting dots through the tunneling process. Morphological investigations have not revealed any effect of the injector well on the dot formation and their size distribution. The optimum TI structure design could be defined.

Data transfer across millimeter-scale electrical wires is limited by both data rates and power density, which creates a performance bottleneck for semiconductor microchips in modern computer systems. Hence, silicon based platforms for optical communication are diligently explored for an on-chip optical data transfer. Semiconductor optical amplifiers provide signal recovery and loss compensation in advanced photonic circuits and are, thus, indispensable components for such platforms. However, silicon photonic components have to operate at much lower voltages and energy-per-bit metrics before it is worth integrating them on-chip with a CPU. The usage of tunnel junctions to control carrier injection can provide a fast and energy-saving alternative. Here, we present experimental results on direct conduction band carrier modulation in the indirect semiconductor Ge by Zener tunnel injection. Electrons are injected by a reverse-biased p-n Zener tunnel diode and recombine radiatively with holes injected by a forward biased p-i-n diode. This injection mechanism favors tunneling of electrons into the direct conduction band valley with concomitant improvements of optoelectronic properties. Benchmarking the performance, 2.42 dB transmission change at 0.9 V bias (1660 nm) at 300 K confirm the working principle. Our device can serve as a starting point to investigate the benefits of tunnel injection for silicon photonic devices.

We propose a tunnel-injection structure, in which WS2 quantum dots (QDs) act as the injector and InGaN/GaN quantum wells (QWs) act as the light emitters. Such a structure with different barrier thicknesses has been characterized using steady-state and time-resolved photoluminescence (PL). A simultaneous enhancement of the PL intensity and PL decay time for the InGaN QW were observed after transfer of charge carriers from the WS2-QD injector to the InGaN-QW emitter. The tunneling time has been extracted from the time-resolved PL, which increases as the barrier thickness is increased. The dependence of the tunneling time on the barrier thickness is in good agreement with the prediction of the semiclassical Wentzel–Kramers–Brillouin model, confirming the mechanism of the tunnel injection between WS2 QDs and InGaN QWs.

A comparison between QD lasers with and without tunnel-injection QW designs was performed. In both cases, six layers of a QD or TI-QD design were grown by molecular beam epitaxy equipped with group-V valved cracker cells. The InAs QDs are embedded in InAlGaAs barriers lattice matched to InP. The TI-QW consists of InGaAs separated by a thin InAlGaAs tunnel barrier. The lasers were processed into broad area and ridge waveguide lasers. Both laser designs exhibited high modal gain values in the range of 10-15 cm−1 per dot layer. The static and dynamic device properties of the different QD laser designs were measured and compared against each other.

F-I-S tunnel junctions of Co2CrAl-I-Pb and Co2Cr0.6Fe0.4Al-I-Pb based on films of semimetal ferromagnetic Heusler alloys Co2CrAl (Curie temperature TC ≈ 334 K) have been fabricated and the features of spin-polarized current in them studied. A theoretical model of spin blocking of the tunnel current shows that the degree of spin polarization of the conduction electrons in quasi-single crystal films of Co2Cr0.6Fe0.4Al and Co2CrAl with B2- and L21-type order is 0.91–0.97.

The spontaneous-emission spectra in the near-IR range (0.8–1.3 μm) from inverted tunnel-injection nanostructures are measured. These structures contain an InAs quantum-dot layer and an InGaAs quantum-well layer, separated by GaAs barrier spacer whose thickness varies in the range 3–9 nm. The temperature dependence of this emission in the range 5–295 K is investigated, both for optical excitation (photoluminescence) and for current injection in p–n junction (electroluminescence). At room temperature, current pumping proves more effective for inverted tunnel-injection nanostructures with a thin barrier (

Dynamic power management at the lowest design level of electronic hardware, i.e. at the device or transistor level, is still a novelty. Instead, energy saving is usually achieved at the circuit level by switching off high performance components and activating low leakage transistors in the current paths. We discuss here performance projections of field-effect transistors providing multiple power modes. A multi-mode (mm) FET can be configured from GHz performance to ultralow leakage by adjusting the charge injection into the transistor channel between thermionic and band-to-band tunnel injection. Nanodevices with ultrathin doping-free channels are the enabler of this novel device concept that requires excellent electrostatic control of the charge type and density. Moreover, nanomaterials with charge carriers of low effective mass will improve the mode tuning of mmFETs. TCAD simulations show that the device current can be switched through nine orders of magnitude at a supply voltage of . The mmFET can also operate in a low dynamic power mode with reduced drive currents but delay times that still allow sub-MHz operation. These properties make mmFETs a promising technology for low power circuitry supplied only by energy harvesters. The possibility to further decrease the supply voltage by integrating a ferroelectric layer in the capacitor stack is also addressed.

In this work the effect of tunneling probability on the modulation and distortion characteristics of tunnel injection transistor laser (TI-TL) are analyzed. The eight level rate equations for three quantum well TI-TL are numerically solved by fourth order Runge–Kutta method. The tunneling injection is denoted by a factor of ‘f’ and it is varied between 0 and 1. Threshold current, modulation bandwidth, modulation depth, IMD3, IMD5 and SFDR are analyzed for different tunneling factors. The threshold current is found to reduce by increasing the tunneling factor. A minimum threshold current of 4.235 mA is obtained for the tunneling factor 0.6. A modulation bandwidth of 5.8 GHz is obtained for classical state and it is increased to 17.9 GHz and 19 GHz for the tunneling factors of 0.6 and 1 respectively with a bias current of 2I Bth . A modulation depth of 0.83 and 0.87 are obtained for tunneling factors 0.6 and 1 respectively. A minimum third and fifth order intermodulation distortion of -39.42 dBc and -48.5 dBc is predicted for the same tunneling factor. The harmonic and intermodulation distortions are found to reduce by increasing the tunneling probability. SFDR of 77.29 dB Hz 2∕3 and 74.49 dB Hz 2∕3 are obtained for IMD3 with and without tunnel injection.

Tunnel-injection lasers promise advantages in modulation bandwidth and temperature stability in comparison to conventional laser designs. In this paper, we present results of a microscopic theory for laser properties of tunnel-injection devices and a comparison to a conventional quantum-dot laser structure. In general, the modulation bandwidth of semiconductor lasers is affected by the steady-state occupations of electrons and holes via the presence of spectral hole burning. For tunnel-injection lasers with InGaAs quantum dot emitting at the telecom wavelength of 1,55$\mu$m, we demonstrate that the absence of spectral hole burning favors this concept over conventional quantum-dot based lasers., Comment: 5 pages, 4 figures

In this paper we have shown a construction of an active sensitive element of irradiation sensor. This sensor is based on metal-insulator-semiconductor structures (MIS structures). In this work we have researched an influence of α-particles to the MIS structures, which were in the mode of the constant current maintaining. This mode is characterized by the high-field Fowler-Nordheim injection. We have shown that ionization processes occurring in dielectric films of MIS structures, which are in the mode of charging and discharging of capacitance and also in the mode of high-field tunnel injection of electrons by pulse of constant current, could be used in order to register the irradiation. We have found out advantages and disadvantages of utilization of MIS sensors to register charged particles. We also have advised how to use these layers.

Transistor laser (TL) is already an established potential candidate for high speed optical interconnects and present day optical communication networks. This paper investigates theoretically the possibility of having lower base threshold current density and enhanced modulation bandwidth by inserting a tunnel injection structure in a TL having multiple quantum wells (MQW) in the base of the heterojunction bipolar transistor. Transfer of injected charge carriers from bulk to low dimensional nano-structure is assumed to occur via virtual energy states, which contributes to the terminal current. Small signal modulation response is obtained by solving the Statz–De Mars laser rate equations. The optimum threshold base current, confinement of carrier, light power outputs etc. are estimated for three QWs positioned at distances of 39, 59, and 79 nm from the emitter-base junction across the base. Incorporation of tunneling structure substantially lowers the base threshold current and increases the modulation bandwidth as compared to usual MQW transistor laser structure. The changes are more prominent with increasing tunneling probability.

The purpose of this study is to investigate the physical mechanism of pulsed-IV degradation under high temperature storage tests. Using the measurements of the pulsed S-parameters immediately after the voltage stress was applied to the GaN-HEMT, we carried out the delay time analysis. As a result, we found that the so-called “virtual gate” region extended toward the drain electrode due to high temperature storage. From this result, we concluded that the electron tunnel injection probability at the gate edge increased and degraded the pulsed-IV characteristics.

In this work we have developed an experimental automatized setup based on PXI platform and LabVIEW by National Instruments to investigate parameters of thin dielectric films of MIS structures. The setup allows to implement the method of high-field tunnel injection of charge carriers under the stress and measurement modes. For the method the main injection of charge into gate dielectric is realized under stress modes at which either voltage, applied to the gate, or current, flowing through the dielectric, is held constant. In order to obtain additional information about changing of charge state of MIS structure one should analyze not only time dependencies of currents and voltages during the stress conditions but, besides, a change of current-voltage characteristics of MIS structure which are acquired before and after injection at measurement level of currents and voltages that are significantly lower than stress levels. As a result, charge effects, which can be observed in MIS structure at the time of stress mode setting, become available to be researched. Besides, that makes possible to take into account an influence of the charge effects to a change of the charge state of gate dielectric under high-field injection of charge carriers.

Tunnel-injection lasers promise various advantages in comparison to conventional laser designs. In this paper, the physics of the tunnel-injection process is studied within a microscopic theory in order to clarify design requirements for laser structures based on quantum dots as active material and an injector quantum well providing excited charge carriers. We analyze how the electronic states of the injector quantum-well and quantum-dot levels should be aligned and in which way their coupling through the tunnel-injection barrier should be adjusted for optimal carrier injection rates into the quantum-dot ground state used for the laser transition. Our description of the tunnel-injection process combines two main ingredients: the tunnel coupling of the wave functions as well as the phonon- and Coulomb-assisted transition rates. For this purpose, material-realistic electronic state calculations for the coupled system of injector quantum well, tunnel barrier, and quantum dots are combined with a many-body theory for the carrier scattering processes. We find that the often assumed longitudinal-optical-phonon resonance condition for the level alignment has practically no influence on the injection rate of carriers into the quantum-dot states. The structural design should provide optimal hybridization of the injector quantum-well states with excited quantum-dot states.

We present the Ge Zener-Emitter injection mechanism for synthesis of an indirect semiconductor optical amplifier (ISOA), featuring gain characteristics and electro-absorption modulation with extinction ratios > 14 dB by sufficient Moss-Burstein shift, for generic Ge-on-Si Photonics platform.

The work has been supported by the grant No. 2013/10/M/ST3/00636 of the National Science Centre in Poland and the QuCoS Project of Deutsche Forschungsgemeinschaft No. RE1110/16‐1. We have investigated optical properties of hybrid two‐dimensional‐zero‐dimensional (2D‐0D) tunnel structures containing strongly elongated InAs/InP(001) quantum dots (called quantum dashes), emitting at 1.55 μm. These quantum dashes (QDashes) are separated by a 2.3 nm‐width barrier from an InGaAs quantum well (QW), lattice matched to InP. We have tailored quantum‐mechanical coupling between the states confined in QDashes and a QW by changing the QW thickness. By combining modulation spectroscopy and photoluminescence excitation, we have determined the energies of all relevant optical transitions in the system and proven the carrier transfer from the QW to the QDashes, which is the fundamental requirement for the tunnel injection scheme. A transformation between 0D and mixed‐type 2D‐0D character of an electron and a hole confinement in the ground state of the hybrid system have been probed by time‐resolved photoluminescence that revealed considerable changes in PL decay time with the QW width changes. The experimental discoveries have been explained by band structure calculations in the framework of the eight‐band k⋅p model showing that they are driven by delocalization of the lowest energy hole state. The hole delocalization process from the 0D QDash confinement is unfavorable for optical devices based on such tunnel injection structures. Publisher PDF

The phenomenon of the emission efficiency droop of InGaN/GaN quantum wells (QWs) in light-emitting diode p-n structures is studied. The influence exerted by two basic processes on the emission efficiency is considered: tunnel injection into a QW and incomplete lateral carrier localization in compositional fluctuations of the band-gap width in InGaN. The sharp efficiency peak at low currents and the rapid efficiency droop with increasing current are due to tunneling leakage currents along extended defects, which appear as a result of a local increase in the electron hopping conductivity via the depletion n region and a corresponding local decrease in the height of the injection p barrier. A less sharp efficiency peak and a weak, nearly linear, decrease in efficiency with increasing current are caused by incomplete lateral carrier localization in the QW due to slowing-down of the carrier energy-relaxation rate and to the nonradiative recombination of mobile carriers.

The characteristics of 1.55 μm InAs self-organized quantum-dot lasers, grown on (001) InP substrates by molecular beam epitaxy, have been investigated. Modulation doping of the dots with holes and tunnel injection of electrons have been incorporated in the design of the active (gain) region of the laser heterostructure. Large values of To=227 K (5°C ≤ T ≤ 45°C) and 100 K were derived from temperature dependent measurements of the light-current characteristics. The modal gain per dot layer is 14.5 cm-1 and the differential gain derived from both light-current and small-signal modulation measurements is ~ 0.8×10-15 cm2. The maximum measured -3 dB small-signal modulation bandwidth is 14.4 GHz and the gain compression factor is 5.4×10-17 cm2. The lasers are characterized by a chirp of 0.6 Å for a modulation frequency of 10 GHz and a near zero α-parameter at the peak of the laser emission. These characteristics are amongst the best from any 1.55 μm edge-emitting semiconductor laser.

The experimental current-voltage characteristics and dependences of the external quantum yield on the current density of light-emitting diodes based on InGaN/GaN multiple quantum wells for the wide temperature range T = 10–400 K are presented. It is shown that, at low-temperatures T < 100 K, the injection of holes into the quantum wells occurs from localized acceptor states. The low-temperature injection of electrons into p-GaN occurs due to quasi-ballistic transport in the region of multiple quantum wells. An increase in temperature leads to an increase in the current which is governed by thermally activated hole and electron injection from the allowed bands of GaN.

The proximity effect in MoRe/Al sandwiches with different critical temperatures T c of MoRe films has been studied. The estimation of the proximity effect parameters has been made and their dependence on the Al thickness built. Features associated with instability of nonequilibrium superconducting state have been observed in the current-voltage characteristics of MoRe/Al–I–Pb tunnel junctions as a result of quasiparticle tunnel injection into the MoRe/Al sandwich. The estimation of the parameter of tunnel injection has been made and its impact on instabilities emergence studied. MoRe–I–Pb tunnel junctions have been produced and their current-voltage characteristics studied to be compared with the results obtained.

Blue-and green-emitting quantum dots have been characterized and ridge waveguide lasers incorporating such quantum dots into the active region have been realized. The laser heteroscturctures were grown by plasma assisted molecular beam epitaxy. Injected carrier lifetimes in the quantum dots have also been measured by temperature dependent and time resolved photoluminescence. A threshold current density of 930 A/cm 2 in the blue-emitting lasers was measured under pulsed bias. A tunnel injection scheme to inject holes has been incorporated in the design of the green quantum dot lasers, and a threshold current density of 945 A/cm 2 in the green-emitting lasers has been measured under pulsed bias. Slope efficiencies of 0.41 W/A and 0.25 W/A have been measured, corresponding to differential quantum efficiencies of 13.9% and 11.3%, in the blue and green lasers, respectively.

We show that GdN nanoislands can enhance inter-band tunneling in GaN PN junctions by several orders of magnitude, enabling low optical absorption low-resistance tunnel junctions (specific resistivity 1.3 X 10-3 {\Omega}-cm2) for various optoelectronic applications. We exploit the ability to overgrow high quality GaN over GdN nanoislands to create new nanoscale heterostructure designs that are not feasible in planar epitaxy. GdN nanoisland assisted inter-band tunneling was found to enhance tunneling in both of the polar orientations of GaN. Tunnel injection of holes was confirmed by low temperature operation of GaN p-n junction with a tunneling contact layer, showing strong electroluminescence down to 20K. The availability of tunnel junctions with negligible absorption could not only improve the efficiency of existing optoelectronic devices significantly, but also enable new electronic and optical devices based on wide band gap materials.

Advanced materials that combine novel functionality and ease of applicability are central to the development of light-emitting diodes (LEDs), which is of ever increasing commercial importance. Here a new metal-insulator-semiconductor (MIS) LED structure that combines economical fabrication with novel device properties is reported. The presented MIS-LED consists of a graphene electrode on p-GaN substrate separated by an insulating SiO2 layer. It is found that the MIS-LED possesses a unique tunability of the electroluminescence spectra depending on the bias conditions. Tunnel injection from graphene into the p-GaN can explain the difference in luminescence spectra under forward and reverse bias. The demonstrated MIS-LED expands the use of graphene and also possibly allows the direct integration of light emitters with other circuit elements.

InGaN/GaN multiple quantum well light emitting diodes with charge asymmetric resonance tunneling structure, which can emit dual color lights of blue/green or blue/yellow, were grown on sapphire by metalorganic chemical vapor deposition. Their optical and structural properties are studied by high-resolution X-ray diffraction, high-resolution transmission electron microscopy, temperature-dependent photoluminescence (PL) and photoluminescence excitation (PLE). PL peak shifts and PLE features are found to vary with the well-growth temperature. The luminescence mechanism is discussed in details, correlating to the In composition fluctuation, carrier localization and the quantum confined Stark effect.

The results of studying the influence of the finite tunneling transparency of injection barriers in light-emitting diodes with InGaN/GaN quantum wells on the dependences of the current, capacitance, and quantum efficiency on the p-n junction voltage and temperature are presented. It is shown that defectassisted hopping tunneling is the main transport mechanism through the space charge region (SCR) and makes it possible to lower the injection barrier. It is shown that, in the case of high hopping conductivity through the injection barrier, the tunnel-injection current into InGaN band-tail states is limited only by carrier diffusion from neutral regions and is characterized by a close-to-unity ideality factor, which provides the highest quantum and power efficiencies. An increase in the hopping conductivity through the space charge region with increasing frequency, forward bias, or temperature has a decisive effect on the capacitance-voltage characteristics and temperature dependences of the high-frequency capacitance and quantum efficiency. An increase in the density of InGaN/GaN band-tail states and in the hopping conductivity of injection barriers is necessary to provide the high-level tunnel injection and close-to-unity power efficiency of high-power light-emitting diodes.