PHOTOLUMINESCENT PROPERTIES OF UNDOPED AND PR-DOPED GAAS EPILAYERS

The various degrees of incorporation of praseodymium (Pr) into GaAs du ring liquid-phase epitaxy (LPE) growth from a Ga-rich solution were in vestigated by low temperature photoluminescence (PL) measurements. The PL spectrum of the undoped (background) GaAs epilayer shows four diff erent peaks which are considered to be due to an intense transition be tween exciton and neutral donor (DX), an intense transition between ex citon and neutral acceptor (AX), a transition of electron-acceptor (eA ) recombination and a weak transition from recombination of donor-acce ptor (DA), respectively. Variations of the different peaks with amount of Pr doping are detailed in the text. Generally we found that the PL spectra of the low Pr-doped GaAs epilayer demonstrate an obvious gett ering effect on the donor-related peaks. As to the spectra of high Pr- doped epilayers, a defect-related (dX) emission peak was produced. Thu s, for the purpose of purification, low Pr-doped (X(Pr) ratio less tha n 0.05%) is suggested. Examination of electrical properties illustrate s that all the Pr-doped samples exhibit p-type conduction. Depending o n the extend of Pr doping in the growth melts, GaAs epilayers have hol e concentrations ranging from 10(15) to 10(16) cm(-3) and with corresp onding hole mobilities varying from 380 to 50 cm(2)/V . s. The electri cal data also reveal that the undesired donor impurities are gettered by Pr ions during LPE growth, but the Pr-related defects formed in hig h Pr-doped melts may act as scattering centers and cause their mobilit ies to decrease.