The quantum confined Stark effect has been investigated in InGaAs/InP quantum wires with widths down to 20 nm. The wires were fabricated by electron beam lithography and wet chemical etching using titanium as mask material. By metalorganic vapor phase epitaxy overgrowth high quantum efficiencies are achieved even for very narrow wire structures. We observe blue shifts in the luminescence peak energy up to 20 meV due to lateral quantization. After evaporating a semitransparent 50 Å thick gold Schottky contact we observe red shifts of the luminescence energy up to 25 meV due to the quantum confined Stark effect by applying a reverse bias voltage of typically 1 V.
The fs-electroabsorption signal in a superlattice modulator designed for 1.55 mm reveals incoherent and coherent transport dynamics in Wannier-Stark states. Bloch oscillations appear chirped due to dynamic field screening.
The design and fabrication using low-pressure metalorganic vapor phase epitaxy (LP-MOVPE) of a HEMT on InP substrate that only uses InP and In/sub x/Ga/sub 1-x/As as layer materials are reported. Lattice-matched (x=0.53) and strained (x=0.68) channels and a double-heterojunction design were used in this investigation. The DC performance of the 0.8- mu m devices at 300 and 77 K was excellent for both cases. Improvements of 9 and 22% in g/sub mext/ with the strain were measured at the same temperatures, in accordance with theoretical predictions. The approach described may serve as a very useful alternative, especially in MOVPE growth, to InAlAs containing structures because it eliminates many of the troublesome effects such as kinks, deep levels, interface states, high output conductances, and gate leakage, which are to a large extent attributed to impurity-Al interactions. The use of lattice-mismatched InGaAs as channel layer increases the conduction band offset to InP, the DH structure improves both confinement and current, and the p-InP barrier layer results in sufficiently high quasi-Schottky barriers.< >
The normalized noise power density is shown for HFETs with InAlAs as barrier layer and those where InP is used. All transistors were manufactured in our Institute using the same geometrical parameters and exhibit almost the same sheet carrier concentration in the channel. The depicted spectrum of the HFET containing InAlAs is a typical result for these devices grown by MBE as long as no degeneration effects occur. On the other hand, HFETs without aluminium which were grown by LP-MOVPE and in which the In mole fraction has been varied from 53% up to 81%, show excellent device properties. The comparison between both material systems reveals that noise of the HFET with InAlAs is slightly lower. This can be understood since during the growth of the interface in this device only one component must be exchanged. Also, due to the larger conduction band discontinuity the penetration depth of the 2DEG into the barrier is reduced and with it the activation of traps located there. The latter also explains the decreasing noise power with increasing indium portion in the channel of the aluminium-free HFETs. However, at 67% indium, the minimum is reached and further increasing the strain does not improve the noise properties. Concluding, it may be stated that there exists a trade-off dependent on the special application between the slightly better performance of the InAlAs/InGaAs/InP HFETs and those devices with a InP barrier, which are less sensitive to stress.
High-performance pseudomorphic InP/InxGa1-xAs/InP backside-doped split-channel heterostructure field-effect transistors (BDSCh-HFETs) with a strained undoped In0.75Ga0.25P Schottky-barrier enhancement layer are reported. Devices with mushroom-shaped gates (LG = 0.25 µm) demonstrated at 300 K maximum extrinsic transconductances of gm = 510 mS/mm and current cutoff frequencies of fT = 102 GHz coupled with off-state drain-source breakdown voltages of VDSbr= 10 V. At 18 GHz a unilateral power gain of 25.6 dB was measured, corresponding to fmax > 200 GHz.
