Jae-Hyun Ryou

Room-temperature continuous photopumped laser operation of coupled InP quantum dot and InGaP quantum well InP–InGaP–In(AlGa)P–InAlP heterostructures

Data are presented demonstrating continuous 300 K photopumped InP quantum dot (QD) laser operation (656–679 nm) realized by modifying and coupling, via tunneling, an auxiliary InGaP quantum well (QW) to the QDs of an InP–In(AlGa)P–InAlP heterostructure grown by metalorganic chemical vapor deposition. The In0.49Ga0.51P QW coupled to the InP QDs by a thin (≲20 A) In0.5Al0.3Ga0.2P barrier overcomes the limitations of carrier collection, lateral transport, and thermalization in the QDs, thus yielding a different form of QD laser.

Coupled InP quantum-dot InGaP quantum well InP–InGaP–In(AlGa)P–InAlP heterostructure diode laser operation

Data are presented showing that a p–n InP–In0.5Ga0.5P–In0.5(Al0.3Ga0.2)P–In0.5Al0.5P quantum-dot (QD) heterostructure diode, with an auxiliary ∼20 A InGaP quantum well (QW) coupled via an In(AlGa)P barrier (∼20 A) to the single layer of QDs to aid carrier collection, has a steeper current–voltage characteristic than the case of a similar diode with no auxiliary QW. The p–n InP+InGaP QD+QW diode is capable of 300 K visible-spectrum QD laser operation, while the single-layer InP QD diode (single QD layer) saturates at low current (≲1 mA) and does not exhibit stimulated emission.

Photopumped red-emitting InP/In0.5Al0.3Ga0.2P self-assembled quantum dot heterostructure lasers grown by metalorganic chemical vapor deposition

We report the 300 K operation of optically pumped red-emitting lasers fabricated from InP self-assembled quantum dots embedded in In0.5Al0.3Ga0.2P layers on GaAs (100) substrates grown by metalorganic chemical vapor deposition. Quantum dots grown at 650 °C on In0.5Al0.3Ga0.2P layers have a high density on the order of 1010 cm−2 and the dominant size of individual quantum dots ranges from ∼5 to ∼10 nm for 7.5 monolayer “equivalent growth.” These InP/In0.5Al0.3Ga0.2P quantum dot heterostructures are characterized by atomic force microscopy, high-resolution transmission electron microscopy, and photoluminescence. Laser structures are prepared from wafers having two vertically stacked InP quantum dot active layers within a 100-nm-thick In0.5Al0.3Ga0.2P waveguide and upper and lower 600 nm InAlP cladding layers. We observe lasing at λ∼680 nm at room temperature in optically pumped samples.

High-density InP self-assembled quantum dots embedded in In0.5Al0.5P grown by metalorganic chemical vapor deposition

We describe the characteristics of high-density InP self-assembled quantum dots embedded in In0.5Al0.5P cladding layers grown at 650 °C on GaAs (100) substrates by metalorganic chemical vapor deposition. Quantum dots grown with different deposition times are characterized by atomic force microscopy, photoluminescence, and transmission electron microscopy. For certain growth conditions, we observe the formation of a high density of quantum dots on the order of 1010 cm−2. The quantum dot average height increases from ∼5 to ∼25 nm with deposition time, while the quantum dot density changes insignificantly. Photoluminescence (4 K) shows a gradual shift of emission spectral peak from 2.06 eV (for 7.5 ML) to 1.82 eV (for 22.5 ML), corresponding to changes in the dominant quantum dot size. Also, incoherent quantum dot formation is not observed for up to 15 ML growth.

Properties of InP self-assembled quantum dots embedded in In0.49(AlxGa1−x)0.51P for visible light emitting laser applications grown by metalorganic chemical vapor deposition

We have studied the properties of InP self-assembled quantum dots embedded in various In0.49(AlxGa1−x)0.51P matrix layers to optimize the growth condition of the quantum dots and structures for III-phosphide quantum-dot-based lasers operating in visible spectral regions. Self-assembled quantum dot-related structures are grown by low-pressure metalogranic chemical vapor deposition and characterized by atomic-force microscopy, high-resolution transmission-electron microscopy, and photoluminescence. High density (∼1010 cm−2) and conveniently sized (∼5×20 nm) quantum dots are produced by growth condition optimization. We find that the quantum-dot heterostructure with a In0.49(AlxGa1−x)0.51P matrix layer having the largest direct band gap produces the most efficient luminescence at room temperature. Laser structures are prepared using optimized growth conditions and matrix materials. Laser operation with lasing wavelengths λ=650–680 nm are demonstrated at 77 and 300 K by optical pumping.

Imaging and local current transport measurements of AlInP quantum dots grown on GaP

Individual AlInP self-assembled quantum dots grown on a (100) GaP substrate are imaged and probed using ballistic electron emission microscopy (BEEM). The excellent nanometer scale lateral resolution of BEEM is utilized to inject carriers directly into a single quantum dot, and thus, current transport through the dot investigated without any direct electrical contact. The BEEM spectra taken on and off the dot revealed a local conduction-band offset between GaP and AlInP with a barrier height of ΔEc∼0.13±0.01 eV.

Observation of resonant tunneling through a quantized state in InP quantum dots in a double-barrier heterostructure

A direct spectroscopic signature associated with the quantized state of the charge carriers in three-dimensionally confined InP quantum dots (QDs) is reported using a ballistic electron emission microscopy (BEEM)/spectroscopy technique. The self-assembled InP QDs are sandwiched in an AlInP double-barrier heterostructure. The excellent nanometer-scale lateral resolution of the BEEM technique is used to investigate the current transport mechanism by the direct injection of electrons into a single quantum dot. The BEEM spectra taken on and off the dot revealed the presence of a localized state at around 0.1±0.02 eV above the ground state.

Self-Assembled Iii-Phospide Quantum Dots Grown by Metalorganic Chemical Vapor Deposition

We report InP self-assembled quantum dots embedded in In 0.51 Al 0.49 P grown by metalorganic chemical vapor deposition. Growth parameters are altered to study the InP quantum-dot growth characteristics under various growth conditions. Quantum-dot morphology is characterized using atomic-force microscopy. Also, photoluminescence studies of the light-emitting properties are performed. Direct-bandgap ternary In x Al I−x P ( x =˜0.7, ˜0.85) self-assembled quantum dots are also grown and compared with InP quantum dots.

Electron transport through strongly coupled AlInP/GaInP superlattices

Using ballistic-electron-emission spectroscopy, electron transport through the principal (Γc,Lc) miniband of an (Al0.5In0.5P)11/(Ga0.5In0.5P)10 superlattice in the strong-coupling regime has been observed. Second derivative spectra of experimental data and Monte Carlo simulations were in agreement.

(Invited) III-Nitride Heterojunction Field-Effect Transistors and Heterojunction Bipolar Transistors for Next-Generation Power Electronics

This presentation will discuss recent progress in technology development for two key III-Nitride (III-N) transistor technologies: high-voltage AlGaN/GaN heterojunction field-effect transistors (HFETs) and GaN/InGaN RF heterojunction bipolar transistors (HBTs). While high-frequency AlGaN-GaN HEFTs have been extensively studied and developed, the high-voltage, highcurrent density III-N electronic devices have been less well investigated. For low-cost high-voltage III-N HFET development, we investigated power transistors built on sapphire substrates and have achieved a 10-A power handling capability with a blocking voltage of up to 1 kV. Using similar transistor processing techniques, we also achieved AlGaN/GaN HFETs with a drain breakdown voltage (BVds) > 1.6 kV, an on-state drain current handling capability of 2.5 A, and a specific onresistance of (Rds(ON)A) 800 V, it is clear that GaN HFETs show a drastic reduction of the on-state resistance by at least a factor of 100 when compared to silicon counterparts. The reported switching performance of the fabrication power switches are among the best results for any GaN-on-Si HFETs reported to date.