Improvement of InGaP/GaAs Heterointerface Quality by Controlling AsH 3 Flow Conditions
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ier. Thus, the InGaP/(In)GaAs interface quality is quite important to get high device performance. EXPERIMENTAL growth GaAs and InGaP layers were grown on 3GaAs interval InGaP inch-diameter (100) GaAs substrate by low pressure (60 Torr) metal organic chemical vapor deposition , AMiH (MOCVD) at a growth temperature of 500 'C. Both TMG .a 3cover layers were 3000-A thick and doped to 1 to 2 x 10 " on cm -'. InGaP layers were grown in the disordered AsH 3 state to obtain high AEc [6] and their energy gap at TEG ,n room temperature was 1.9 eV, which was determined by photoluminescence (PL) measurement. InGaP layers were lattice matched to GaAs layers and the TMI on SPH.ug In-composition determined from X-ray diffraction measurements was 0.48. PH 3*of The gas flow sequence at the growth interval was as follows, (1) AsH3 was continuously supplied - Time to cover GaAs after the Ga source was switched off. (2) After the AsH-4 flow was stopped, PH3 purge gas was switched on to remove AsH3 from around the Fig. 2 Gas flow sequence for growth sample. (3) After that, InGaP source gases were of the InGaP/GaAs structure. GaAs surface was covered with AsH and supplied. The timing of these gas changed at the subsequently purged by PH at3 the 3 growth interval is shown in Fig. 2. In this study, the GaAs-to-InGaP growth interval. PH 3 AsH 3 cover time and flow rate were changed to flow conditions were kept constant investigate the influence of As on the interface (300 cc/min and 2.5 min). characteristics. The PA purge time was fixed at 2.5 min and the P1 flow late was fixed at 300 cc/min. Schottky diodes with a 280 jtrm x 280 itm Ti/Au Schottky electrode encircled by a AuGe/Ni ohmic electrode were fabricated to measure the electrical characteristics. We measured the carrier concentration profile around the interface using C-V measurement. To avoid break down at the deep bias condition, we also fabricated diodes after etching off about half the thickness of the InGaP layer. Since the interface morphology can not be observed in situ at the time of MOCVD, we observed the GaAs surface by AFM after removing the InGaP layers selectively by the HC1. The observation was performed in air using the tapping mode of Digital Instrument's Nanoscope III. RESULTS AsH. cover time dependence AsH3 cover time dependence on the heterointerface parameters was compared between 2 samples whose AsH3 cover times were 0.05 (#2174) and 2.5 min (#2172). The AsH 3 flow rate was fixed at 100 cc/min. The carrier concentrations around the InGaP/GaAs interface for these samples are respectively shown in Figs. 3(a) and (b), by solid lines. These apparent carrier concentration profiles are quite different and the difference is related to the AsIH3 cover time. The electron depletion at the interface region in the InGaP layer is annihilated in the sample with the 2.5 min cover time. We determined the conduction band offset, AEc, and interface charge density, a, at the interfaces from these carrier concentration profiles using Kroemer's method [7]. Although the interface pos
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