Shawn R. Gibb

High Output Power from 260 nm Pseudomorphic Ultraviolet Light-Emitting Diodes with Improved Thermal Performance

This letter reports on the improved performance of a pseudomorphic ultraviolet light-emitting diode (LED). At 100 mA input current, 9.2 mW of quasi-CW output power was measured in a calibrated integrating sphere. The addition of a heat sink, required for CW and higher power operation, introduced a numerical aperture of 0.86, and 72 mW was measured in pulsed mode at 1.7 A, indicating that the total output power exceeds 100 mW when corrected by the coupling factor. The high characteristic temperature of 983 K was instrumental in achieving these record output powers for an LED with wavelength shorter than 265 nm.

270 nm Pseudomorphic Ultraviolet Light-Emitting Diodes with Over 60 mW Continuous Wave Output Power

In this letter, the achievement of over 60 mW output power from pseudomorphic ultraviolet light-emitting diodes in continuous wave operation is reported. Die thinning and encapsulation improved the photon extraction efficiency to over 15%. Improved thermal management and a high characteristic temperature resulted in a low thermal rolloff up to 300 mA injection current with an output power of 67 mW, an external quantum efficiency (EQE) of 4.9%, and a wall plug efficiency (WPE) of 2.5% for a single-chip device emitting at 271 nm in continuous wave operation.

Properties of Mid-Ultraviolet Light Emitting Diodes Fabricated from Pseudomorphic Layers on Bulk Aluminum Nitride Substrates

High quality bulk aluminum nitride substrates were used to obtain pseudomorphic AlxGa1-xN layers with low dislocation density, smooth surfaces, and high conductivity. These layers were fabricated into mid-ultraviolet light emitting diodes with peak wavelengths in the range of 240–260 nm. The low dislocation density of the pseudomorphic quantum wells resulted in improved performance over previously published data. The output powers of the on-wafer measurements were greater than 5 mW in continuous wave operation, and 16 mW in pulsed operation. This was achieved utilizing single die (with an active area of 1×10-3 cm2).

High power, high efficiency, AlGaN/GaN HEMT technology for wireless base station applications

We report AlGaN/GaN high-electron-mobility-transistors (HEMT) on SiC substrates with field modulation plates (FP) of various dimensions and different gate widths. As a measure of the status of GaN technology achieved in this work, small periphery 150 μm HEMT demonstrated a continuous wave (CW) output power density of 22.7 W/mm at 2.14 GHz with power added efficiency (PAE) of 54% when biased at a drain-source voltage (V D S ) of 80 V. As a demonstration of the sealability of this technology, a 20-mm-wide device exhibited 100 W CW output power and a simultaneous peak PAE of 55.3% at 2.14 GHz when biased at class AB and V D S =48V. WCDMA measurements on the 20mm part demonstrated ACP of -35 dBc at 42.5 dBm output power and 30% PAE under the same bias condition. Analysis of FP related performance tradeoffs are also presented in this work.

Reliability assessment of AlGaN/GaN HEMT technology on SiC for 48V applications

We present wearout reliability assessment of GaN HEMTs fabricated on SiC. Based on 3 temperature 48 V dc stress tests and using a failure criterion of 10% reduction in Idss, the 60% confidence interval on estimate of Ea was [2.00,2.94] eV and the predicted 60% confidence interval on estimate of MTTF at Tj=200 degC was [1.0 x 106, 3.0 x 107] hours. To compare the impact of dc and RF stress, additional experiments were conducted on a smaller sample set and the results indicate that the impact of dc and RF stress is not significantly different.

Performance and RF Reliability of GaN-on-SiC HEMT's using Dual-Gate Architectures

AlGaN/GaN HEMTs on SiC have been fabricated with dual and single gate device geometries. Subthreshold characteristics and drain bias dependence of large signal parameters were compared to identify differences in electric field. Degradation under RF stress reveals the relative impact of temperature and electric field. The results illustrate the beneficial effects of the dual gate geometry for performance and reliability

GaN Wide Band Power Integrated Circuits

Gallium nitride (GaN) amplifiers have demonstrated very high power density as well as wide bandwidth in previous research. This paper examines their use in supplying flat gain, power, and linearity across a large bandwidth. It demonstrates two types of power amplifiers: a Ft Doubler (FT2) amplifier and a Cascode amplifier, both of which require a simple PCB tune. Both amplifiers show 0.2 to 4GHz bandwidth with 30 dBm PldB output power. The 3GPP WCDMA output power is 20 dBm at -45 dBc ACLR. Also, a WiMAX design is presented for the 3.2-3.8 GHz band to show the feasibility of a GaN HEMT amplifier in a relatively broad band, high linearity commercial application, with 27 dBm output at 2% EVM

High-power pseudomorphic mid-ultraviolet light-emitting diodes with improved efficiency and lifetime

Recent advances in mid-ultraviolet light-emitting diodes grown pseudomorphically on bulk AlN substrates have led to improved efficiencies and lifetimes. For a 266 nm device an output power of 66 mW at 300 mA has been achieved with an external quantum efficiency of 4.5%. More importantly, the lifetimes of these devices have been increased substantially. Testing of LEDs in both surface mount design (SMD) and TO-39 packages show L50 lifetimes well in excess of 1,000 hours under a variety of case temperatures and currents. Package-related catastrophic failures are eliminated through encapsulation and hermetic sealing, further reducing failure rates and extending the lifetime.

Status of GaN HEMT performance and reliability

This report will focus on the status of GaN HEMT based amplifier technology development at RFMD. This technology is based around GaN on semi-insulating SiC substrates for optimal thermal performance. RFMDs 0.5μm gate technology features high performance advanced field plate structures, including a unit power cell producing high gain (21dB), high power density (3-5W/mm at 28V) and high efficiency (65-70 percent) at cellular frequencies. We will report on transistor and module performance relevant to applications ranging from high power, high bandwidth amplifiers, to switches and ICs for radar, electronic warfare, cellular infrastructure and homeland security. Additionally, we will report on reliability results that demonstrate capability for dependable, high voltage operation.

Linearity and Efficiency Performance of GaN HEMTs with Digital Pre-Distortion Correction

The linearity and efficiency performance was studied for large periphery AlGaN/GaN HEMTs. Comparison was made between inherent linear device performance and device performance using digital pre-distortion (DPD) correction. Additionally, both drain voltage and current were optimized to provide high efficiency for a specified linearity. Significant improvements in linear efficiency were achieved using the DPD correction with a best measured PAE of 43.5 %, at a Vd of 28 V, using two carrier W-CDMA