Alo.6 GaO•4 As heterojunctions

While emphasis has been placed on coherent heterojunctions for high speed device structures, the use of mismatched layers unstrained via misfit dislocations has been limited. Yet, in certain cases, the misfit dislocated layer can be advantageous. For example, in the growth of GaAs on Ina.53 GaO.47 As it has been shown that the misfit dislocations can be isolated to the GaAs interface region suggesting the integration of optoelectronic and high speed logic devices. I Alternatively, Ina.4 Gao.6 As has been grown on GaAs substrates yielding high performance 1.3 /-Lm metal-semiconductor-metal (MSM) detectors which can be integrated with high speed GaAs devices. In fact, the incorporation of a misfit dislocated layer in the active portion of heterojunction bipolar transistors has resulted in higher gain devices compared to those in which a pseudomorphic layer was used. 3 In this work, a misfit dislocated Ina.75 GaQ.25 As/ Ala.6 GaOA As heterojunction was investigated, since its properties are efficacious for the implementation of a semiconductor, resistive gate GaAs channel charge-coupled device. As depicted in Fig. 1, a resistive gate charge-coupled device (RGCCD) employs a resistive layer which acts as a continuous potential divider between spaced phase electrodes, ensuring that the charge moves under the constant influence of an electric field.4 Conventional RGCCDs utilize a ceramic metallic (cermet) compound whose composition must be carefully controlled to ensure proper optical and electrical properties. 5 The use of a semiconductor resistive gate, however, exploits the compositional control and uniformity inherent in molecular beam epitaxy (MBE). In addition, novel device structures, such as an internal photoemission CCD imager, can be implemented since the band offset between the resistive and channel layer can be controlled through proper selection of materials. The InGaAsl AIGaAs heterojunction was chosen since the small band gap, high electron affinity InGaAs suggests a large band offset to AIGaAs,6 yielding a low leakage structure. Furthermore, nonalloyed ohmic contact formation to air-exposed InGaAs containing a large In mole fraction is facilitated by the Fermi level being pinned near the conduction band,7 which simplifies the RGCCD fabrication process. This paper reports the basic electrical properties of this severely mismatched heterojunction. The heterojunction shows rectification and in one sample exhibited a 1.0 eV barrier height. The low mobility observed in the InGaAs layer is attributed to defects, and is advantageous for the RGCCD application.