InGaP/GaAs hole barrier asymmetry determined by (002) X-ray reflections and p-type DB-RTD hole transport

Evaluation of the composition of the interlayer at the inverted interface in InGaP/GaAs heterojunctions

“…In the literature basically two compounds have been proposed to be the interlayer alloy, i.e., In x Ga 1−x As [8,14,18,19] and In x Ga 1−x As 1−y P y [7,8,10,13,20,21]. The formation of either one of these two compounds has been reported to be strongly affected by the growth conditions, such as growth interruption or not, duration of the PH 3 purge after stopping the growth of InGaP, duration of the As H 3 pre-flow before TMGa is introduced, intentional interposition of some extra layer etc [7,8,10,13,14,[18][19][20][21].…”

“…InGaP/GaAs has a low conduction band offset that makes it very suitable for HBTs [9]. However, the InGaP/GaAs system has the drawback that an extra interlayer spontaneously forms at the GaAs-on-InGaP interface (inverted interface) [7][8][9][10][12][13][14][15][16][17][18][19][20][21]. The causes suggested in the literature for its formation are three: In carry-over, As/P exchange and P/As intermixing at the location of the inverted interface [7][8][9][10][12][13][14][15][16][17][18][19][20][21].…”

“…Only a very few papers reported on its presence [6,22]. Photoluminescence (PL) has shown that an emission at a wavelength longer than the ones of GaAs and InGaP is always associated with the extra interlayer [7,10,[12][13][14][15][16][17][18]. Often this peak has an intensity much higher than the GaAs and InGaP peaks making the latter ones disappear.…”

“…Due to its smaller band gap the interlayer has a strong effect on the electric transport and optical properties of the structures/devices because the excess electron-hole pairs are localized and recombine in the extra interlayer [12,17] so that it contributes more effectively to the radiative decay of the excited minority carriers than the GaAs well. It was also proven by I-V characteristics that the asymmetry between the normal and inverted interfaces results in different hole-barrier functionality [18]. The hypothesis of Liu et al [24] that the long wavelength peak can be ascribed to the spatially indirect transition due to the type-II band alignment of the InGaP/GaAs heterojunction does not seem convincing [13].…”

“…The nature and composition of the interlayer are still controversial. Besides PL, several other techniques, like X-ray diffraction [12,16,[18][19][20], electrical methods [24,25] scanning tunneling spectroscopy [26] were employed to investigate the properties of the interlayer at the GaAs-on-InGaP interface. Transmission electron microscopy (TEM) was applied in some works to get information on the overall structure of the InGaP/GaAs samples [6,8,19,20,27,28], but detection and information right of the interlayer was not reported apart from the paper by Hsieh et al where the interlayer was detected by Scanning TEM (STEM) [7].…”