More and more attention has been paid to the quaternary AlGaInP alloy

which is the novel candidate materials for visible light and short-wave-length optoelectronic devices and solar cells and which has largest direct band-gap among semiconductors matched to GaAs. In this article

the temperature-dependent and excitation-intensity-dependent photoluminescence(PL) spectra are applied to investigate the (Al

x

Ga

1-x

)

0.51

In

0.49

P(

x

=0.29) alloys lattice-matched to GaAs

grown by metalorganic vapor phase epitaxy(MOVPE). The temperature of samples were kept at 19K during the measuring of excitation-dependent PL spectra with the laser intensity varied within 3 orders of magnitude.For the temperature-dependent spectra

the temperature was changed from 19K to 250K. According to D.J.Mowbray et al.'s results

the turning-point from direct-band to indirect-band of (Al

x

Ga

1-x

)

0.51

In

0.49

P lies in

x

=0.50

the (Al

x

Ga

1-x

)

0.51

In

0.49

P(

x

=0.29) alloys show direct-band gap character and a certain ordering structure for the large separation of PL peak energy and the band-gap derived from the empirical equation of Mowbray and for the relatively wider linewidths than the disordered alloys. The PL peak is excitation independent

which might imply there exists no spatially separated centers in direct band-gap quaternary (Al

x

Ga

1-x

)

0.51

In

0.49

P alloys

but shows anomalous temperature behavior

where the PL peak energy changes with temperature and exhibits Z-shape dependence. The PL peak energy decreases with increasing temperature from 19K

a blue-shift of PL peak energy occurs between 55K and 84K

afterwards

the PL peak energy decreases monotonously again. To the best of our knowledge

this is the first time the temperature anomaly is reported for (Al

x

Ga

1-x

)

0.51

In

0.49

P(

x

=0.29) alloys

which confirms the existence of ordering structure in (Al

x

Ga

1-x

)

0.51

In

0.49

P(

x

=0.29) alloys in another way.Because the superlattice effect resulted from the ordering structure can lead to both the band-folding effect of conduction band from the L-point to the Γ-point in the Brillouin zone and the splitting of crystal valence-band so as to lead to the separation of light-and heavy-hole band in valence band

our further study shows

however

no valence-band splitting in (Al

x

Ga

1-x

)

0.51

In

0.49

P(

x

=0.29) alloys

so we speculate

due to the influence of the ordering structure which results in the band-folding effect in the Brillouin zone

the carriers in conduction band get enough energy to transfer from the Γ-band to the L-band when the temperature is above 55K

thus

the temperature anomaly occurs.Above 84K

the carriers from the L-band dominate the luminescence and abide by the general thermal decay principle.