AlGaN/GaN high electron mobility transistor, AlGaAs/InGAs/GaAs pseudomorphic HEMT, and InAlAs/InGaAs metamorphic HEMT ͑MHEMT͒ epitaxial structures have been characterized using surface photovoltage spectroscopy. The effects of the transistor top and bottom delta-doping levels ␦ top , ␦ bot , and surface charge Q sur on the spectrum features have been studied using numerical simulations. Based on the latter, an empirical model has been developed, which allows extraction and comparison of ␦ top , ␦ bot , and Q sur and is applicable for both double-sided and single-sided delta-doped structures. Prediction of the final device performance by the model is shown for two MHEMT structures. Devices produced on these structures show maximum drain currents, which correlate well with ␦ top values calculated using the model.
Suppression of surface segregation of silicon dopants during molecular beam epitaxy of ( 411 ) A In 0.75 Ga 0.25 As ∕ In 0.52 Al 0.48 As pseudomorphic high electron mobility transistor structures
Light emission from power transistors at a compression level in the range of 2-3 dB has been imaged using a microscope-mounted camera. Results show that the emitted light intensity distribution across the transistor is highly nonuniform and depends on the load impedance, direct current, and RF conditions. The light intensity correlates with a negative gate current, which is a result of the RF-induced impact ionization in the transistors. The nonuniformity in the light intensity is attributed to the RF-induced voltage overstress in the transistors. The observed light emission may be used as a direct and contactless monitor of the RF-induced overstress in transistors and power amplifiers.Index Terms-Breakdown, high-power amplifier (HPA), impact ionization, light emission, parasitic oscillations, power transistor.
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