Growth and Characterization of Piezoelectrically Enhanced Acceptor-Type AlGaN/GaN Heterostructures
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F99W11.8 Downloaded from https://www.cambridge.org/core. IP address: 80.82.77.83, on 28 Dec 2017 at 16:10:34, subject to the Cambridge Core terms of use, available at https://www.cambridge.org/core/terms. https://doi.org/10.1557/S1092578300004828
This paper examines the extent of piezoelectric acceptor doping and modulation doping and compares these results with conventional Mg acceptor doping in AlGaN/GaN system. Material characterization including the Mg concentration profile and AlGaN/GaN interface, as determined by secondary electron mass spectrometry (SIMS), are discussed in relation to the sheet conductivity of the films. EXPERIMENTAL PROCEDURE Each heterostructure consisted of a GaN (0001) film grown at 1000ºC on an AlxGa1-xN (0001) layer. The latter was deposited at 1020ºC on an AlN (0001) buffer layer previously deposited at 1100ºC on an on-axis 6H-SiC (0001) substrate. Figure 1 shows the doping and Al profiles of the GaN and AlxGa1-xN layers in selected samples. xAl 20% 10% [Mg] 2E19
xAl 20% 10% [Mg] 2E19
800 1300 Depth (A) Sample A xAl 20% 10% [Mg] 2E19
xAl 20% 10% [Mg] 2E19 800 1300 Depth (A) Sample B
No AlGaN
800 1300 Depth (A) Sample C
xAl 20% 10% [Mg] 2E19 75 800 1300 Depth (A) Sample D
75 800 1300 Depth (A) Sample E
Figure 1. Doping and Al profiles in selected GaN/AlxGa1-xN heterostructures. The zero point of the depth scale is the top of the GaN layer. The AlN buffer layer and all subsequent films were grown in a cold-wall, vertical, pancake-style, RF inductively heated metalorganic vapor phase epitaxy (MOVPE) system. Ammonia (NH3), triethylaluminum (TEA) and triethylgallium (TEG) were used as precursors. Bis-cyclopentadienyl-magnesium (Cp2Mg) was employed for the p-type doping. High-purity H2 was used as both the carrier and the diluent gas. After cooling to room temperature the samples were annealed at 800°C in N2 to activate the Mg acceptors. Additional details of the growth experiments in the NCSU reactor have been previously reported [8]. Sample A contains all doping contributions: piezoelectric (PZ), modulation doping (MD) and conventional acceptors (ACC). Sample B lacks the modulation doping component. Sample C is an Mg-doped GaN film and is the control sample. It has no PZ charge or modulation doping. Sample D has doping from MD and PZ. Sample E has only PZ doping. The Mg concentration profiles and the Al concentrations were determined using Secondary Ion Mass Spectrometry (Cameca IMS-6f) having a 100nA 10keV O 2+ primary beam. Sputtering rates and Mg sensitivity factors for varying Al concentrations have been previously determined [9]. Analysis of the AlGaN/GaN interface was conducted by comparing the Al and Ga signals. Electrical measurements of the films
F99W11.8 Downloaded from https://www.cambridge.org/core. IP address: 80.82.77.83, on 28 Dec 2017 at 16:10:34, subject to the Cambridge Core terms of use, available at https://www.cambridge.org/core/terms. https://doi.org/10.1557/S1092578300004828
were conducted using CV and Hall measurements (van der Pauw configuration). The A
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