Photoreflectance temperature dependence of graded InAlAs/InGaAs heterojunction bipolar transistor layers
Journal
Journal of Applied Physics
Journal Volume
78
Journal Issue
6
Pages
4035-4038
Date Issued
1995
Author(s)
Abstract
Photoreflectance(PR) spectra of the graded InAlAs/InGaAs heterojunction bipolar transistor layers were investigated at various temperatures between 8 K and 300 K. The energy features of the PR spectra were fitted and identified as band-to-band transitions in the graded layers which were grown by pulsed molecular beam epitaxy (pulsed-MBE) and InGaAs as well as InAlAs layers. The temperature variation of energy gaps can be described by the Varshni and Bose-Einstein equations. A linear variation relationship of band gaps with Al composition (z) was observed and approximated to be E0(z)=0.809+0.769z eV at T=0 K. However, the parameters aB and ΘB derived from the Bose-Einstein expression do not change meaningfully in the whole range of Al composition. From the observed Franz-Keldysh oscillations (FKOs) we have evaluated the built-in dc electric fields in the i-InGaAs collector, i-InGaAs spacer and n-InAlAs emitter regions. The electric fields are in good agreement with the continuity condition of electric displacements in the interfaces between emitter and base.
SDGs
Type
journal article