Deriving of Single Intensive Picosecond Optical Pulses from a High-Power Gain-Switched Laser Diode by Spectral Filtering

Single 25 ps/16 W optical pulses were achieved by spectral filtering from a multiheterostructure gain-switched laser diode with its quasisteady-state modes suppressed by a factor of 103 as compared with the peak power. A significant transient spectrum broadening makes this possible provided that a very high dI/dt rate of the pumping current pulse is used. A simple numerical model is suggested which describes adequately both the spectral and transient features of the observed phenomenon. It follows from the model that single picosecond optical pulses can be obtained from any type of high power semiconductor laser

The 1.6-Kv AlGaN/GaN HFETs

The breakdown voltages in unpassivated nonfield-plated AlGan/GaN HFETs on sapphire substrates were studied. These studies reveal that the breakdown is limited by the surface flashover rather than by the AlGan/GaN channel. after elimination of the surface flashover in air, the breakdown voltage scaled linearly with the gate-drain spacing reaching 1.6 kV at 20 mu m. The corresponding static ON-resistance was as low as 3.4 m Omega(.)cm(2). This translates to a power device figure-of-merit V-BR(2)/R-ON = 7.5 x 10(8) V-2 . n(-1) cm(-2), which, to date, is among the best reported values for an AlGan/GaN HFET

III-Nitride Transistors with Capacitively Coupled Contacts

AlGaN∕GaNheterostructure field-effect transistor design using capacitively coupled contacts (C3HFET) is presented. Insulated-gate [C3 metal-oxide-semiconductor HFET(C3MOSHFET)] has also been realized. The capacitively coupled source, gate, and drain of C3 device do not require annealedOhmic contacts and can be fabricated using gate alignment-free technology. For typical AlGaN∕GaNheterostructures, the equivalent contact resistance of C3 transistors is below 0.6Ωmm. In rf-control applications, the C3HFET and especially the C3MOSHFET have much higher operating rf powers as compared to HFETs.C3 design is instrumental for studying the two-dimensional electron gas transport in other wide band gap heterostructures such as AlN∕GaN, diamond, etc., where Ohmic contact fabrication is difficult

Silicon Dioxide-Encapsulated High-Voltage AlGaN/GaN HFETs for Power-Switching Applications

In this letter, new approach in achieving high breakdown voltages in AlGan/GaN heterostructure field-effect transistors (HFETs) by suppressing surface flashover using solid encapsulation material is presented. Surface flashover in III-Nitride-based HFETs limits the operating voltages at levels well below breakdown voltages of GaN. This premature gate-drain breakdown can be suppressed by immersing devices in high-dielectric-strength liquids (e.g., Fluorinert); however, such a technique is not practical. In this letter, AlGan/GaN HFETs encapsulated with PECVD-deposited SiO2 films demonstrated breakdown voltage of 900 V, very similar to that of devices immersed in Fluorinert liquid. Simultaneously, low dynamic ON-resistance of 2.43 m Omega. cm(2) has been achieved, making the developed AlGan/GaN HFETs practical high-voltage high-power switches for power-electronics applications

Digital Oxide Deposition of SiO\u3csub\u3e2\u3c/sub\u3e Layers for III-Nitride Metal-Oxide-Semiconductor Heterostructure Field-Effect Transistors

We present a digital-oxide-deposition (DOD) technique to deposit high quality SiO2dielectric layers by plasma-enhanced chemical vapor deposition using alternate pulses of silicon and oxygen precursors. The DOD procedure allows for a precise thickness control and results in extremely smooth insulating SiO2 layers. An insulating gate AlGaN∕GaNheterostructurefield-effect transistor(HFET) with 8nm thick DOD SiO2dielectric layer had a threshold voltage of −6V (only 1V higher than that of regular HFET), very low threshold voltage dispersion, and output continuous wave rf power of 15W∕mm at 55V drain bias

Two Mechanisms of Blueshift of Edge Emission in InGaN-Based Epilayers and Multiple Quantum Wells

We present the results of a comparative photoluminescence(PL) study of GaN and InGaN-based epilayers, and InGaN/GaN multiple quantum wells(MQWs). Room-temperature PL spectra were measured for a very broad range of optical excitation from 10 mW/cm2 up to 1 MW/cm2. In contrast to GaN epilayers, all In-containing samples exhibited an excitation-induced blueshift of the peak emission. In addition, the blueshift of the emission in the InGaN epilayers with the same composition as the quantum well was significantly smaller. The comparison of the blueshift in the “bulk” InGaN and in the MQWs allowed us to separate two different mechanisms responsible for this effect: (i) filling of the localized states in In-rich areas and (ii) screening of the polarizationelectric field in strained MQW structures

Low-Loss High Power RF Switching Using Multifinger AlGaN/GaN MOSHFETs

We demonstrate a novel RF switch based on a multifinger AlGan/GaN MOSHFET. Record high saturation current and breakdown voltage, extremely low gate leakage current and low gate capacitance of the III-N MOSHFETs make them excellent active elements for RF switching. Using a single element test circuit with 1-mm wide multifinger MOSHFET we achieved 0.27 dB insertion loss and more than 40 dB isolation. These parameters can be further improved by impedance matching and by using submicron gate devices. The maximum switching power extrapolated from the results for 1a/mm 100 mum wide device exceeds 40 W for a 1-mm wide 2-a/mm MOSHFET

Enhanced Luminescence in InGaN Multiple Quantum Wells with Quaternary AlInGaN Barriers

We report on the comparative photoluminescence studies of AlGaN/GaN, GaN/InGaN, and AlInGaN/InGaN multiple quantum well(MQW) structures. The study clearly shows the improvement in materials quality with the introduction of indium. Our results point out the localized state emission mechanism for GaN/InGaN structures and the quantum well emission mechanism for AlInGaN/InGaN structures. The introduction of indium is the dominant factor responsible for the observed differences in the photoluminescence spectra of these MQW structures

Luminescence Mechanisms in Quaternary Al\u3csub\u3ex\u3c/sub\u3eIn\u3csub\u3ey\u3c/sub\u3eGa\u3csub\u3e1-x-y\u3c/sub\u3eN Materials

Low-temperature photoluminescence investigations have been carried out in the quaternary AlInGaN epilayers and AlInGaN/AlInGaN multiple quantum wells (MQWs) grown by pulsedmetalorganic chemical-vapor deposition (PMOCVD). With increasing excitation power density, the emission peaks in both AlInGaN epilayers and MQWs show a strong blueshift and theirlinewidths increase. The luminescence of the samples grown by PMOCVD is attributed to recombination of carriers/excitons localized at band-tail states. We also demonstrate theluminescence properties of AlInGaN and AlGaN materials grown by a pulsed atomic-layerepitaxy and conventional MOCVD, respectively

Accumulation Hole Layer in p-GaN/AlGaN Heterostructures

We present the results on piezoelectric and pyroelectricdoping in AlGaN-on-GaN and GaN-on-AlGaN heterostructures and demonstrate p-GaN/AlGaN structures with accumulation hole layer. Our results indicate that polarization charge can induce up to 5×1013 cm−2 holes at the AlGaN/GaN heterointerfaces. We show that the transition from three-dimensional (3D) to two-dimensional (2D) hole gas can be only achieved for hole sheet densities on the order of 1013 cm−2 or higher. At lower densities, only 3D-hole accumulation layer may exist. These results suggest that a piezoelectrically induced 2D-hole gas can be used for the reduction of the base spreading resistance in AlGaN/GaN-based heterostructurebipolar transistors