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This paper analyzes the performance and reliability of deep-ultraviolet light-emitting diodes (LEDs) on AlGaN emitting at 280 and 295 nm. By means of detailed electroluminescence characterization, we show that the optical properties of the LEDs are strongly influenced by the presence of deep-level-related radiative transitions, and we separately evaluate the contribution of each of these recombination mechanisms on the overall light emission. The reliability analysis presented in this paper shows that stress determines the gradual decrease of the output power of the LEDs, which is more prominent at low measuring current levels. Degradation is attributed to the increase of the nonradiative recombination rate. By means of C-V analysis, we give evidence of modifications of the charge distribution in the active layer, taking place as a consequence of stress: this mechanism is considered to be related to the generation of new defect states near/within the active region. [ABSTRACT FROM PUBLISHER]

We have fabricated and characterized lateral current injection (LCI) ridge-waveguide lasers formed by ion-implanted injectors. Comprehensive optical and electrical measurements have been performed over a wide temperature range (10 K-300 K) on two sets of lasers with differing ridge widths and active region structures. Several new phenomena unique to the LCI mechanism have been observed, including a positive differential resistance kink at threshold, and inverse temperature-dependencies of quantum efficiency and threshold current at cryogenic temperatures. Electron-hole mobility disparity, local carrier nonpinning above threshold due to photon-assisted ambipolar diffusion, and intrinsically higher current densities have been identified as the major factors governing these LCI laser characteristics. The results have important implications for future LCI laser design and ultimate performance [ABSTRACT FROM PUBLISHER]

We report on the low-loss microwave switch monolithic microwave integrated circuit (MMIC) built using voltage-controlled capacitors formed by the two Schottky contacts deposited over an AlGaN/GaN heterostructure. A symmetrical structure of the varactor allows for either positive or negative control voltage. A small electrode and a spacing size of 2 \mu\m ensure low on-impedance. The fabricated series–shunt switch MMIC shows 0.8-dB insertion loss and 28-dB isolation at 18 GHz and the maximum linear power of 34 dBm at 10 GHz and 38 dBm at 18 GHz (extrapolated from 2- to 10-GHz data). The device does not require contact alignment or annealing; it is robust, simple to fabricate, and well suited for MMICs. [ABSTRACT FROM AUTHOR]

We show that III-nitride radio-frequency switches with a composite slow/fast gate have higher maximum switching power and breakdown voltage compared with conventional switches of the same type. The composite gate design includes an additional “slow gate” electrode formed under the metal gate using a low-conducting InGaN layer. The “slow gate” covers the entire source–drain spacing. The addition of the “slow gate” layer not only offers a lower insertion loss and higher isolation but, as shown in this letter, also increases the power handling capability by “delaying” switch self-modulation under high-power stress. We also show that, the “slow gate” design increases breakdown voltage. [ABSTRACT FROM AUTHOR]

We present a novel approach to reduce the off-state capacitance of microwave transistor switches. The new design includes a “slow gate” layer, which allows for complete depletion of the channel in the source–drain region, thus reducing the gate–channel capacitance. Due to very high impedance at high frequencies, the “slow gate” shunting effect and its own capacitance contributions are negligibly small. This novel approach is validated by demonstrating an AlGaN/GaN single-pole double-throw switch with the “slow gate” layer formed by InGaN film. The new gate design decreases the insertion loss of the fabricated switch by approximately 0.5 dB and increases the isolation by approximately 5 dB. [ABSTRACT FROM AUTHOR]

We propose a high-frequency extension of the transmission line model method that allows for independent extraction of open-surface sheet resistance of a semiconductor layer and that under metallization. The method is applied for the characterization of an AIGaN/GaN heterostructure with a high (~40%) Al content with and without a top dielectric layer. In both cases, the sheet resistance under the metal is approximately 30% smaller than that under the open surface. This reduction is attributed to the surface charge compensation by the top metal. [ABSTRACT FROM AUTHOR]

We report on an integrated low-loss, high-isolation RF switch using large periphery AIGaN/GaN heterostructure field-effect transistors (HFETs) connected in a Γ-cell configuration. The insertion loss was below 0.27 dB and isolation exceeded 28 dB in the frequency range from direct current to 2 GHz. The unit-width ON resistance of large periphery HFETs was slightly higher than that of narrower devices due to current crowding in the metal electrodes. Modeling of the observed current crowding effect predicts that an optimized design will yield less than a 0.1 dB insertion loss, which is comparable to the best RF MEMS. [ABSTRACT FROM AUTHOR]

A comparative study of the dynamic current-voltage (DI-V) characteristics of III-N heterojunction and double heterojunction field-effect transistors (HFETs and DHFETs) reveals that the current and RF power collapse in HFETs arise from modulation of device series resistances under large input signal. The model based on space-charge limited current through the depletion regions formed at the gate edges due to the charge trapping explains the DI-V behavior and other observations related to the RF current collapse in III-N HFETs. [ABSTRACT FROM AUTHOR]

We present the characteristics of a quarter-micron gate metal-insulator-semiconductor heterostructure field-effect transistor (MISHFET) with Si[sub 3]N[sub 4] film as a gate insulator. A detailed comparison of the MISHFET and an identical geometry HFET shows them to have the same radio frequency (RF) power gain and cut-off frequency, while the MISHFET has much lower gate-leakage currents and higher RF powers at operating frequencies as high as 26 GHz. The MISHFET gate-leakage currents are well below 100 pA at gate bias values from -10 V to +8 V. At zero gate bias, the drain saturation current is about 0.9 A/mm and it increases to 1.2 A/mm at +8 V gate bias. The output RF power of around 6 W/mm at 40 drain bias was found to be frequency independent in the range of 2 to 26 GHz. This power is 3 dB higher than that from HFET of the same geometry. The intrinsic cutoff frequency is ∼63 GHz for both the HFET and the MISHFET. This corresponds to an average effective electron velocity in the MISHFET channel of 9.9 × 10[sup 6] cm/s. The knee voltage and current saturation mechanisms in submicron MISHFETs and heterostructure field-effect transistors (HFET) are also discussed. [ABSTRACT FROM AUTHOR]

The authors report the output RF signal distortions in the novel SiO[sub 2]-AlGaN-InGaN-GaN metal-oxide-semiconductor double heterostructure FET (MOSDHFET) device structure. Their comparative studies of MOSDHFETs and Schottky gate type DHFETs fabricated on the same wafer show significantly improved RF output signal linearity in MOSDHFETs at high-input signals. At the RF output powers close to saturation, the relative level of the second and third harmonic powers in MOSDHFETs was found to be less than -30 dB, which is about 15-20 dB lower as compared to identical geometry DHFET. This improvement is attributed to a better linearity of the MOSDHFET current-gate voltage characteristics. [ABSTRACT FROM AUTHOR]