Optical and electrical characterization of an AlGaAs/GaAs heterostructure

Abstract

Photoreflectance (PR) spectroscopy and Hall-effect measurements have been used for the analysis of a molecular beam epitaxially grown AlGaAs/GaAs heterostructure. The photoreflectance spectrum provided valuable information regarding the quality of the undoped GaAs, the aluminum composition of the AlGaAs layers, impurity diffusion, and the quantum well widths. Successive layer removal aided with the identification of some photoreflectance features and provided insight into the electrical transport properties of the heterostructure. Quantum well widths obtained from PR lineshape fits are compared with layer thicknesses measured from cross-sectional transmission electron micrographs.

Photoreflectance spectra from GaAs HEMT structures reinvestigated: solution of an old controversy

“…A weak electric field in the GaAs buffer layer was used by another group of authors to explain the SPOs of the PR spectra in terms of FK oscillations [6,8,9,12,14,18]. Support for this interpretation was lent by etching experiments.…”

“…Photoreflectance (PR) spectroscopy is now widely used for the study and characterization of semiconductor device structures, like heterojunction bipolar transistors, high electron mobility transistors (HEMTs) and quantum well lasers [1]. Much attention has been paid to the PR investigations of HEMT structures with either GaAs [2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19][20] or InGaAs [1,15,16,[20][21][22][23][24][25][26][27][28][29][30] forming the high-mobility region of the device. The PR spectra from InGaAsbased HEMTs show features which are clearly due to optical transitions in the channel region [1].…”

Room temperature polarized photoreflectance characterization of GaAlAs/InGaAs/GaAs high electron mobility transistor structures including the influence of strain relaxation

“…22,23 From the FKOs associated with the GaAs signal, we deduce a field of about 15Ϯ1 kV/cm, due to Fermi level pinning at the substrate buffer interface. 24 The FKOs associated with the GaAlAs feature are due to the large, almost uniform electric field in the portion of the samples caused by the difference in the Fermi level at the surface and in the Si ␦-doped layer. From these FKOs we obtain a field of 160Ϯ10 kV/cm which is consistent with a midgap surface Fermi level.…”

Contactless Electroreflectance Study of InxGa1-xAs/InP Multiple Quantum Well Structures Including the Observation of Surface/Interface Electric Fields

“…Given the low background doping level in the InP regions it is difficult to account for the observed electric fields based on space charge considerations. Therefore, in order to explain the results for the various electric fields we suggest that in our structures the Fermi level is pinned (a) at the top of the valence band at the substrate/buffer interface, probably by carbon [20), (b) at the top of the conduction band at the MQW/buffer layer interface and (c) at 0.3 V below the conduction band at the free surface [21]. Based on the dimensions of the cap layer (1500A) the surface electric field is 20 kV/cm, in good agreement with the field associated with the f 3 structure.…”