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ABSTRACT: We report on the optoelectronic properties of Al0.25Ga0.75N/GaN-based ultraviolet (UV) photodetectors for the application as a high current, high gain optical switch. Due to an internal gain mechanism combined with the high conductivity of the two-dimensional electron gas at the heterostructure interface, photocurrents in the milliampere-range were obtained with UV illumination. By employing a mesa structure design with meander geometry very low dark currents below 50 nA up to a bias voltage of 100 V were achieved. Optical switching with an on/off-current-ratio of five orders of magnitude was demonstrated. The response time was determined to be 6 ms and persistent photoconductivity was observed. The photodetector is visible-blind with a cut-off wavelength of 365 nm according to the band gap energy of the GaN absorption layer. A high responsivity with a maximum of 70 A/mW at 312 nm and 100 V bias voltage was demonstrated.
Applied Physics Letters 05/2011; 98(21):211114-211114-3. · 3.84 Impact Factor
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ABSTRACT: By means of step stressing tests on AlGaN/GaN HEMTs the robustness properties of devices fabricated on wafers with different buffer designs have been compared to each other (standard UID GaN buffer and UID Al0.05Ga0.95N back-barrier in combination with GaN channel layer). The devices with GaN buffer showed an abrupt increase of gate leakage current after reaching drain bias values in the range of 30 V while devices with Al0.05Ga0.95N back-barrier did not show any degradation up to 120 V drain bias. All DC-Step-Stress tests have been accompanied by Electroluminescence (EL) analysis and electrical characterization techniques before, during and after stress. It has been shown that EL at forward and reverse bias conditions can be used as an indicator of potential device degradation. Devices comprising an AlGaN back-barrier design demonstrated superior robustness.
Microelectronics Reliability. 01/2011; 51(2):217-223.
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ABSTRACT: In this work, we investigate the relevance of device geometry to the Schottky gate characteristics of AlGaN/GaN high electron mobility transistors. Changes of three-terminal gate turn-on voltage and gate leakage current on the gate—drain spacing, source—gate spacing and recess depth have been observed. Further examinations comparing device simulations and measurements suggest that gate turn-on voltage is influenced by the distribution of electric potential under the gate region which is related to the geometry. By proper design of the device, high gate turn-on voltage can be obtained for both depletion-mode and recessed enhancement-mode devices.
Semiconductor Science and Technology 06/2010; 25(7):075005. · 1.72 Impact Factor
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ABSTRACT: We present an AlGaN/GaN high-electron mobility transistor (HEMT) with an integrated recessed protection diode on the drain side of the transistor channel. Results from our Schottky-drain HEMT demonstrate an excellent reverse blocking with minor tradeoff in the on-state resistance for the complete device. The excellent quality of the forward diode characteristics indicates high robustness of the recess process. The reverse blocking capability of the diode is better than - 110 V. Physical-based device simulations give an insight in the respective electronic mechanisms. This is the first time that a recessed Schottky-drain diode integrated in a HEMT device is presented.
IEEE Electron Device Letters 10/2009; · 2.85 Impact Factor
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ABSTRACT: DC-Step-Stress-Tests of GaN HEMTs have been performed on wafers with and without GaN-cap. The tests consist of a step ramping of drain-source voltage V<sub>DS</sub> by 5 V every two hours at off-state. The irreversible evolution of leakage current starting at a certain drain voltage has been taken as a criterion for the onset of device degradation. It has been stated that there is a stability limit for V<sub>DS</sub> depending on the epitaxial design. It has been found that wafers with GaN cap show much higher critical voltages as compared to non-capped epitaxial designs. Electroluminescence measurements have been performed to localize defects after DC-Step-Stress-Tests up to 80 V for wafer without GaN cap and 120 V for wafer with GaN cap.
Reliability Physics Symposium, 2009 IEEE International; 05/2009
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ABSTRACT: This paper presents a study of the capability of gallium-nitride (GaN) high-electron mobility transistors (HEMTs) to achieve low noise and high linearity performance. A packaged GaN HEMT was measured in a 50 - Omega system at 2 GHz. Noise figures slightly above 1.8 dB were achieved together with a record third-order intercept point of 54 dBm. The same configuration yields a maximum output power of 30 W, with 50% power-added efficiency. This combination of high power and low-noise performance allows the realization of highly linear low-noise amplifiers, which could significantly reduce protection and filter efforts at receiver inputs.
IEEE Microwave and Wireless Components Letters 10/2008; · 1.72 Impact Factor
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G. Sonia,
F. Brunner,
A. Denker, R. Lossy,
M. Mai,
J. Opitz-Coutureau,
G. Pensl,
E. Richter,
J. Schmidt,
U. Zeimer,
L. Wang,
M. Weyers,
J. Wrfl,
G. Trnkle
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ABSTRACT: Operation of AlGaN/GaN HFETs in space was simulated by irradiation with protons and heavy ions at 68 MeV and 2MeV and fluences up to 10<sup>13</sup> cm<sup>-2</sup>. Before and after irradiation dc and pulsed I-V characteristics of the AlGaN HFET devices were measured. A thick GaN reference layer was characterized by photoluminescence, X-ray diffraction and Hall measurements before and after irradiation. The results of the material characterization correlate with the device results. High energy (68 MeV) irradiation has no impact on device performance while high fluences at lower energy (2 MeV) result in degradation
IEEE Transactions on Nuclear Science 01/2007; · 1.45 Impact Factor
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ABSTRACT: Progress in fabrication of packaged discrete L- and X-band power AlGaN/GaN HFETs is presented. By exploiting typical GaN HFET related features such as improved linearity, power density, gain and broad band capability the devices allow for novel architectures for base stations in mobile communications and for space applications. Highlights to be presented are L-band power bar devices designed for continuous wave (cw) operation delivering an cw output power of 30 W and 100 W with 20 dB and 14 dB linear gain respectively. The architecture of these devices is based on novel gate "feed plate" structures. Furthermore discrete, hermetically packaged X-band devices for space based SSPAs in the power range of 10 W (continuous wave) at 8 GHz are presented
Microwave Conference, 2006. 36th European; 10/2006
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ABSTRACT: Vertical interconnect accesses (VIAs) were fabricated between the source electrode on the front and the ground on the backside of high-power microwave AlGaN/GaN high-electron mobility transistors (HEMTs) on ∼400-μm-thick silicon carbide substrates. Through-wafer microholes with an aspect ratio of up to ∼ 8 were drilled using pulsed UV-laser machining and subsequently metallized using electroplating. The successful implementation of the laser-assisted VIA technology into device processing was proven by dc and RF characterization. When biased at 26 V, a saturated output power of 41.6 W with an associated power-added efficiency of 55% at 2 GHz was achieved for a 20-mm AlGaN/GaN HEMT with through-wafer VIAs.
IEEE Electron Device Letters 07/2006; · 2.85 Impact Factor
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G. Sonia,
E. Richter, R. Lossy,
M. Mai,
J. Schmidt,
M. Weyers,
G. Tränkle,
A. Denker,
J. Opitz-Coutureau,
G. Pensl,
I. Brauer,
H. P. Strunk
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ABSTRACT: AlGaN/GaN heterojunction field effect transistors (HFETs) have been irradiated with protons at 68 MeV and 2 MeV with fluences up to 1013 cm–2 in order to simulate operation in space. Hall effect measurements, dc characteristics and RF load pull measurements at 2 GHz do not reveal significant changes indicating the suitability of the transistors for reliable operation in space. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)
physica status solidi (c) 05/2006; 3(6):2338 - 2341.
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ABSTRACT: AlGaN/GaN HEMTs are promising devices for very high power applications. These transistors present high breakdown voltages and have already shown their ability to operate at high temperature. But their power performances are limited because of the presence of traps within the material, decreasing the drain current density. In order to predict the loss of power density and quantify trapping effects, simulations need to be performed with a suitable model, which accounts for these parasitic trapping effects. This paper deals with the characterization, modeling and simulation of trapping effects and power behavior of a 1 mm GaN device on a SiC substrate. Experimental results are compared to the simulations.
Microwave Symposium Digest, 2003 IEEE MTT-S International; 07/2003
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ABSTRACT: AlGaN/GaN HEMTs processed by 2 inch stepper lithography in a production line environment are presented. The uniformity of the HEMTs is assessed, showing an excellent homogeneity of electrical properties over the wafer. Typical values for maximum saturation current, transconductance and pinch-off voltage are: 616 mA/mm, 203 mS/mm, —3.5 V with very good homogeneity across 2″. The cut off frequencies FT and Fmax are 23 and 57 GHz, respectively. Standard deviations across the wafer for the dc properties are below 3%.
physica status solidi (a) 11/2001; 188(1):263 - 266. · 1.21 Impact Factor
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ABSTRACT: High quality GaN/(Al,Ga)N based heterostructures have been grown on SiC(0001) by reactive molecular beam epitaxy (RMBE) using ammonia as nitrogen precursor. These multilayer structures exhibit atomically smooth surfaces and abrupt interfaces. Based on this achievement, we study here the capability of RMBE to fabricate devices requiring abrupt interfaces, namely, distributed Bragg reflectors (DBRs) and heterostructure field-effect transistors (HFETs)
Compound Semiconductors, 2000 IEEE International Symposium on; 02/2000
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ABSTRACT: DC and RF characteristics of AlGaN/GaN HEMTs processed by 2-inch stepper lithography are presented. The devices, grown by MOVPE on 2" sapphire wafers consist of: GaN buffer, Al<sub>0.25</sub>Ga<sub>0.75 </sub>N spacer, doped Al<sub>0.25</sub>Ga<sub>0.75</sub>N supply layer, Al<sub>0.25</sub>Ga<sub>0.75</sub>N barrier, GaN cap. Refractory source and gate contacts along with mesa isolation and air bridge technology are applied. Typical values for maximum saturation current, transconductance and pinch-off voltage are: 616 m/A/mm, 203 mS/mm, -3.5 V with very good homogeneity across 2". The cut off frequencies f<sub>T </sub> and f<sub>max</sub> are 24 and 54 GHz respectively. A standard small signal equivalent circuit model exactly describes DC- and microwave properties
Compound Semiconductors, 2000 IEEE International Symposium on; 02/2000
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G. Sonia,
E. Richter,
F. Brunner,
A. Denker, R. Lossy,
M. Mai,
F. Lenk,
J. Bundesmann,
G. Pensl,
J. Schmidt,
U. Zeimer,
L. Wang,
K. Baskar,
M. Weyers,
J. Würfl,
G. Tränkle
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ABSTRACT: AlGaN/GaN heterostructure field effect transistors (HFETs) were irradiated with 2 MeV protons, carbon, oxygen, iron and krypton ions with fluences ranging from 1 × 109 cm−2 to 1 × 1013 cm−2. DC, pulsed I–V characteristics, loadpull and S-parameters of the AlGaN HFET devices were measured before and after irradiation. In parallel, a thick GaN reference layer was also irradiated with the same ions and was characterized by X-ray diffraction, photoluminescence, Hall measurements before and after irradiation. Small changes in the device performance were observed after irradiation with carbon and oxygen at a fluence of 5 × 1010 cm−2. Remarkable changes in device characteristics were seen at a fluence of 1 × 1012 cm−2 for carbon, oxygen, iron and krypton irradiation. Similarly, remarkable changes were also observed in the GaN layer for irradiations with fluence of 1 × 1012 cm−2. The results found on devices and on the GaN layer were compared and correlated.
Solid-State Electronics.
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G. Sonia,
E. Richter,
F. Brunner,
A. Denker, R. Lossy,
F. Lenk,
J. Opitz Coutureau,
M. Mai,
J. Schmidt,
U. Zeimer,
L. Wang,
K. Baskar,
M. Weyers,
W. Würfl,
G Tränkle
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G. Sonia,
E. Richter,
F. Brunner,
A. Denker, R. Lossy,
M. Mai,
F. Lenk,
J Bundesmann,
G. Pensl,
J. Schmidt,
U. Zeimer,
L. Wang,
K. Baskar,
M. Weyers,
J. Würfl,
G Tränkle
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G. Sonia,
E. Richter,
F. Brunner,
A. Denker, R. Lossy,
M. Mai,
F. Lenk,
J. Opitz Coutureau,
G. Pensl,
J. Schmidt,
U. Zeimer,
L. Wang,
K. Baskar,
M. Weyers,
J. Würfl,
G Tränkle
