In GaAs-AlGaAs single and multiple quantum-well (SQW and MQW) ridge lasers, grown by molecular beam epitaxy, the temperature dependence of the threshold current, expressed by the characteristic temperature T0, is investigated as a function of the cavity length (L) at temperatures between 20 °C and 93 °C. SQW lasers, in contrast to MQWs, show at room temperature a strong decrease in T0 from 250 K to about 100 K when the length is reduced from 400 to 200 μm. We found that by further reducing L to about 130 μm, a strong increase in T0 up to 250 K occurs and T0 decreases again to 80 K for 60 μm SQW lasers. This T0 behavior in SQW lasers is directly correlated to the gain saturation of the n=1 transition and the switch of the laser emission to the n=2 transition. In MQW lasers, T0 is constant at all cavity lengths, even at high temperatures, indicating that no gain saturation occurs.
In this paper, the performances of our InP-based and metamorphic HFETs are compared. Measurements on the RF as well as the noise behaviour are presented. Furthermore, first results are demonstrated on the integration of the InP-based PIN diode and HFET on one InP-substrate. Using these two devices, we integrated three different MMIC designs on one wafer: SPDT switch, phaseshifter and a combination of SPDT switch and LNA for a multifunctional MMIC.
We report about a systematic study on the influence of the barrier thickness (LB) and the spacer length (Ls) on the current/voltage behavior of AlAs/GaAs/AlAs resonant tunneling diodes (RTDs) to achieve a high peak current density up) and a low valley current density (iv) for device applications at room temperature. The samples are grown by molecular beam epitaxy. With increasing LB in the range between 3 monolayers (ML) and 6 ML we observe a drastic increase of the peak-to-valley current ratio (PVR = jp'jv) up to a maximum value of 5 (12) at 300 K (77 K) for LB = 6 ML, Simultaneously, j, decreases exponentially with thicker barriers. A maximum available current density in the negative-differential-resistance region of Aj = jp -j, = 165 W c m 2 at 300 K is achieved for 4ML thick AlAs barriers. We found no remarkable influence of the emitter spacer length variation on jp for L, > 10 nm. However, for Ls < 10 nm jp increases with decreasing Ls (maximum improvement of 60 $6 for Ls = 0.5 nm). The PVR can be significantly improved by using a pseudomorphic InGaAs prewell (PW) layer for carrier injection. We observe PVR values of 7.2 at 300K and 27 at 77K. Additionally, jp increases by a factor of 6 in comparison with standard samples without a PW layer. By incorporation of an AlGaAs prebarrier layer we also obtain an improvement of PVR, but the peak current density is reduced. High frequency operation of RTDs is investigated in a waveguide resonator.
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