Abstract-Recent advances in design and technology significantly improved the performance of low-noise InP Gunn devices in oscillators first at -band (110-170 GHz) and then at -band (75-110 GHz) frequencies. More importantly, they next resulted in orders of magnitude higher RF output power levels above -band and operation in a second-harmonic mode up to at least 325 GHz. Examples of the state-of-the-art performance are continuous-wave RF power levels of more than 30 mW at 193 GHz, more than 3.5 mW at 300 GHz, and more than 2 mW at 315 GHz. The dc power requirements of these oscillators compare favorably with those of RF sources driving frequency multiplier chains to reach the same output RF power levels and frequencies. Two different types of doping profiles, a graded profile and one with a doping notch at the cathode, are prime candidates for operation at submillimeter-wave frequencies. Generation of significant RF power levels from InP Gunn devices with these optimized doping profiles is predicted up to at least 500 GHz and the performance predictions for the two different types of doping profiles are compared.

Detailed absorption measurements and the analysis of the absorption spectra of In1−xGaxAs lattice matched to InP are reported. The lattice matching parameter Δa/a covered a range from +4×10−3 to −1×10−3. From the absorption data of material with small matching parameter we obtain the value of the interband matrix element ( P2=20.7 eV), the excitonic Rydberg (Ex =2.5 meV), and damping constant (Γ0=5.1 meV) in the temperature range from 1.5 to 340 K. From the temperature dependent band-gap shrinkage and exciton damping constant Γ, information on the carrier-phonon interaction is obtained. The effect of the biaxial stress in the epitaxial layers caused by the mismatch with the substrate is demonstrated by absorption spectra which directly reveal the valence band splitting due to stress. Absorption measurements on samples with and without substrate indicate that the strained expitaxial layers do not relax completely if the substrate is etched away. The remaining strain field is probably caused by misfit dislocations generated during the epitaxial growth. Taking into account these stress effects, a precise value of the band gap as a function of temperature is derived. At zero temperature, we obtain a value of Eg(0) =821.5±0.2 meV for the band gap of In0.53Ga0.47As. From the absorption spectra we further determine the value of the bimolecular recombination coefficient (B=0.96×10−10 cm3/s at room temperature). The comparison of material grown by molecular-beam epitaxy (MBE) and liquid-phase epitaxy (LPE) shows that there is no difference between significant optical data of LPE and MBE high-quality layers.

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