Photoreflectance as a non-destructive, room-temperature technique for routine testing of PM-HEMT structures

In the context of a comparative study of MBE and MOCVD PM-HEMT structures on 3″ GaAs substrates, utilization of photoreflectance indicated that the technique can provide substantial information both non-destructively as well as at room temperature. Concentrating on the structure of the photoreflectance trace below 1.4 eV, the technique can provide information on the combined effect of thickness and In composition in the InGaAs quantum well. In particular, photoreflectance was found to be especially useful for mapping the uniformity over a single wafer as well as for mapping the reproducibility from wafer to wafer. Representative, characteristic patterns were consistently observed for MBE-grown layers, distinct from equally characteristic patterns of MOCVD-grown layers. More importantly, these patterns, obtained by room temperature photoreflectance, were found to coincide with those obtained by low temperature photoluminescence. Although the two techniques identify different electronic transitions, room temperature photoreflectance proves to be equally well adapted as an acceptance test for layer uniformity as low temperature photoluminescence. In probing the reason of non-uniformities, however, low temperature photoluminescence does provide more information. Experimental results are presented for both MBE and MOCVD PM-HEMT structures as well as information extracted from their treatment by modeling in the quantum wells

Comparative investigation of MBE and MOCVD PMHEMT structures for high frequency applications

This work presents a comparison of DC, RF and power characteristics at high frequency as well as a comparison of the uniformity of these parameters across each wafer in pseudomorphic high electron mobility transistor structures grown by MBE and MOCVD. In either case, both single and double heterostructures grown on 3″ S. I. GaAs substrates were investigated. The comparison revealed that uniformity characteristics are similar, independent of the epitaxial method used or of the type of heterostructure grown, and that device uniformity mapping does not correlate to material uniformity mapping. In terms of power characteristics, double heterostructures exhibited better performance than single heterostructures for both epitaxial methods

Photoreflectance as a non-destructive, room-temperature technique for routine testing of PM-HEMT structures

In the context of a comparative study of MBE and MOCVD PM-HEMT structures on 3″ GaAs substrates, utilization of photoreflectance indicated that the technique can provide substantial information both non-destructively as well as at room temperature. Concentrating on the structure of the photoreflectance trace below 1.4 eV, the technique can provide information on the combined effect of thickness and In composition in the InGaAs quantum well. In particular, photoreflectance was found to be especially useful for mapping the uniformity over a single wafer as well as for mapping the reproducibility from wafer to wafer. Representative, characteristic patterns were consistently observed for MBE-grown layers, distinct from equally characteristic patterns of MOCVD-grown layers. More importantly, these patterns, obtained by room temperature photoreflectance, were found to coincide with those obtained by low temperature photoluminescence. Although the two techniques identify different electronic transitions, room temperature photoreflectance proves to be equally well adapted as an acceptance test for layer uniformity as low temperature photoluminescence. In probing the reason of non-uniformities, however, low temperature photoluminescence does provide more information. Experimental results are presented for both MBE and MOCVD PM-HEMT structures as well as information extracted from their treatment by modeling in the quantum wells

Comparative investigation of MBE and MOCVD PMHEMT structures for high frequency applications

This work presents a comparison of DC, RF and power characteristics at high frequency as well as a comparison of the uniformity of these parameters across each wafer in pseudomorphic high electron mobility transistor structures grown by MBE and MOCVD. In either case, both single and double heterostructures grown on 3″ S. I. GaAs substrates were investigated. The comparison revealed that uniformity characteristics are similar, independent of the epitaxial method used or of the type of heterostructure grown, and that device uniformity mapping does not correlate to material uniformity mapping. In terms of power characteristics, double heterostructures exhibited better performance than single heterostructures for both epitaxial methods

Dependence of arsenic antisite defect concentration and two dimensional growth mode on LT GaAs growth conditions

We investigated the dependence of Arsenic antisite defect concentration and that of epitaxial thickness (tepi), above which a transition to three dimensional growth appears, on the growth conditions of LTGaAs layers grown by MBE. The antisite defect concentration and the lattice expansion of LT layers grown at 180°C-250°C initially increases with increasing pressure ratio PAs4/PGa and then saturates. On the other hand, tepi decreases with increasing PAs4/PGa and depends strongly on the presence of roughness on the substrate surface. Our results indicates that the transition to 3D growth in LT layers is caused by the reduced surface mobility of the atoms impinging on the growth front during the epitaxy. We also determined the optimum LT growth conditions in order to achieve both maximum AsGa concentration (∼ 1.4 × 1020 cm-3) and a smooth surface without a transition to 3D growth. © 1998 Elsevier Science B.V. All rights reserved

Lattice mismatch and conductivity in LTAlGaAs layers

The lattice mismatch of as-grown and annealed Low Temperature (LT) AlxGa1-xAs layers, epitaxially grown by Molecular Beam Epitaxy on (001) S.I. GaAs substrates, has been investigated as a function of growth conditions. The variation of electrical conduction in the temperature range of 150 K to 400 K has also been examined. The relaxed lattice mismatch due to the LT growth increases as the growth temperature decreases and as the V/III equivalent pressure ratio increases. For the same growth conditions the relaxed lattice expansion is higher in the LT GaAs than in the LT AlxGa1-xAs layers. The lattice expansion in LT AlxGa1-xAs decreases by increasing the Al concentration. The conductivity measurements have revealed the presence of hopping conduction in LT AlxGa1-xAs layers (T < 300 K) with a characteristic activation energy Eo increasing from 31 meV to 46 meV as the Al concentration rises from 0.19 to 0.65. The rise in Eo is caused by the high density of acceptor states. These acceptor states can be attributed to gallium vacancies as in the case of LTGaAs layers. The increase in gallium vacancy concentration is consistent with the lower dilation of the lattice constant in the LTAlxGa1-xAs layers compared with that of LTGaAs. © 1998 Elsevier Science B.V. All rights reserved

Uniformity study in PM-HEMT structures and devices by optical and electrical characterization

We have studied the uniformity of both the structure and of the device characteristics of PM-HEMTs on (001) GaAs substrates. The structure uniformity was studied by photoreflectance modulation spectroscopy (PR) at room temperature and photoluminescence spectroscopy (PL) at low temperature. PR was chosen for its main advantages of high sensitivity in room temperature, higher than that of high temperature photoluminescence and non-destructiveness. We have studied the main transitions of the transistor structures using the 2DEG approximation. PR and PL results yield uniformity with relative standard deviation (r.s.d.) lower than 1%. After PR, transistors were fabricated on the wafers and tested for DC and RF characteristics and the results were correlated with the PR data. The comparison between PR and PL has resulted in a strong indication that PR can be the technique of choice for the complete characterization of structure uniformity of 3 inch pseudomorphic heterostructures, since it is non-destructive, relatively simple and can be performed at room temperature. © 1998 Elsevier Science B.V. All rights reserved

Uniformity study in PM-HEMT structures and devices by optical and electrical characterization

We have studied the uniformity of both the structure and of the device characteristics of PM-HEMTs on (001) GaAs substrates. The structure uniformity was studied by photoreflectance modulation spectroscopy (PR) at room temperature and photoluminescence spectroscopy (PL) at low temperature. PR was chosen for its main advantages of high sensitivity in room temperature, higher than that of high temperature photoluminescence and non-destructiveness. We have studied the main transitions of the transistor structures using the 2DEG approximation. PR and PL results yield uniformity with relative standard deviation (r.s.d.) lower than 1%. After PR, transistors were fabricated on the wafers and tested for DC and RF characteristics and the results were correlated with the PR data. The comparison between PR and PL has resulted in a strong indication that PR can be the technique of choice for the complete characterization of structure uniformity of 3 inch pseudomorphic heterostructures, since it is non-destructive, relatively simple and can be performed at room temperature. © 1998 Elsevier Science B.V. All rights reserved

The effect of arsenic overpressure on the structural properties GaAs grown at low temperature

The structural properties of GaAs grown by molecular-beam epitaxy at low temperatures have been investigated by scanning electron microscopy, transmission electron microscopy, and high-resolution x-ray double-crystal rocking curves as a function of arsenic overpressure during growth. It was found that surface smoothness and excess arsenic incorporation both depend strongly on growth temperature and on As/Ga flux ratio, For each growth temperature there is a ‘’window” in the flux ratio which results in smooth surfaces. As-grown layers have an increased lattice constant in the growth direction. This relative lattice expansion increases with flux ratio at a constant growth temperature and eventually saturates, Transmission electron micrographs have revealed the presence of arsenic precipitates in material annealed at 600 degrees C. Increasing the As-4 pressure during growth results in increases in precipitate diameter by almost 50% while their density and shape remain constant. Based on these observations a model has been developed to explain the lattice expansion dependence on arsenic overpressure. (C) 1996 American institute of Physics