Nondestructive determination of beryllium outdiffusion in AlGaAs/GaAs heterojunction bipolar transistor structures by low-temperature photoluminescence

In this work, low-temperature photoluminescence (PL) is used for the invest igation of beryllium (Be) dopant outdiffusion in AlGaAs/GaAs single-heteroj unction bipolar transistors (HBTs). Near the typical emission peak at simil ar to 1.92 eV which is due to the band-to-band transition from AlGaAs emitt er, an additional emission peak is found in the PL spectrum. This peak is f ound to be caused by the Be-related transition from AlGaAs emitter due to t he Be outdiffusion from the GaAs base to the AlGaAs emitter. The concentrat ion of Be outdiffused into the emitter can be estimated from the energy sep aration between these two emission peaks in AlGaAs range based on the band gap narrowing effect. The measured dc current gain and the emitter-base tur n-on voltage of the HBTs fabricated on different wafers with different grow th conditions were found to correlate well with the PL results. Our results demonstrate that low temperature PL technique is an efficient method in id entifying Be outdiffusion in HBTs and is useful in HBT growth and device st ructure optimization. (C) 1999 American Institute of Physics. [S0021-8979(9 9)06320-3].