Recently there has been considerable interest in blue electroluminescence in ZnSe diodes.The most important problem in obtaining good blue electroluminescence diodes is to prepare ZuSe single crystal with high purity and perfection.In ZnSe

copper is an electrical and Optical active impurity and forms deep levels to produce deep center emissions and suppress near-band edge emission.Therefore

it is necessary to study the behavior of copper impurity in ZnSe.Many authors have investigated the Cu-G and Cu-R deep centers in Cu-diffused ZnSe crystals.In this paper

two Cu-doped ZnSe crystals are prepared by the diffusing techniques at low or high temperature

and two deep acceptor levels

E

v

+0.30eV and

v

+0.72eV

related to Cu-G and Cu-R centers are determined for the first time by ODLTS technique

respectively.Nominally undoped ZnSe crystals used in this study were grown from the Vapour phase in sealed capsules containing slight excesses of zinc in our laboratory.Two different methods are used to obtain the superior Cu-G and Cu-R centers respectively.First the Cu impurity was diffused into the ZnSe crystal at high temperature.Dice of undoped ZnSe were annealed in molten Zn-Cu-Al alloy at 850℃ for 100h to reduce their resistivities and Cu-R center was formed at the same time.Second

the Cu impurity was diffused into the ZnSe crystal at low temperature.Copper was deposited on the surface of low resistive and undoped ZnSe dice by vacuum evaporation technique

then the dice are heated in N

2

atmosphere at 400℃ for 20min.Diodes are prepared by making In ohmic contact on one face of a dice and evaporating Au potential barrier electrode on to the opposite face.Fig.1 shows the ODLTS spectrum in ZnSe:Cu

Al crystal diffused at high temperature.Only one peak corresponds to a deep acceptor level with activation energy of E

v

+0.72eV is appeared.A red emission band

which peaked at 6350Åat RT and at 6320Åat LNT

is obtained in electroluminescence spectra as shown in Fig.2

respectively.The peak position of the red emission band corresponds to that of Cu-R emission band.Fig.3 shows the time resolved spectra of red emission band in ZnSe:Cu

Al crystal at 77K.This spectrum gradually shifts to the low energy direction as a whole with decay time.It indicates that the recombination process of the red band ascribes to D-A pair transition.According to the results mentioned above it is reasonable to think that the deep acceptor level of E

v

+0.72eV obtained in ODLTS spectrum should be attributed to the acceptor related to Cu-R center.The value of E

v

+0.72eV is in good agreement with that measured by Grimmeiss using thermally stimulated capacitance method.Fig.4 shows the ODLTS spectra in Cu-doped and undoped ZnSe crystals heated in N

2

atmosphere at 400℃ for 20min.Comparing Cu-doped and undoped ZnSe crystals

it is found that the concentration of E

v

+0.30eV remarkably increases and the concentration of E

v

+0.72eV also increases for the Cu-doped ZnSe crystal.Fig.5 shows that the concentrations of all deep levels except E

c

-0.33eV decrease with increasing the reverse bias.Fig.6 shows the electroluminescence spectra at RT and LNT in Cu-doped ZnSe diffussed at low temperature.In EL spectrum at 77K

there is a strong green emission band peaked at 5300Åbesides the near band edge emission.Two emission bands peaked at 6350Åand 4650Åare appeared in the EL spectrum at RT.The peak position of the red and green bands are similar to that of the Cu-R and Cu-G centers reported by Stringfellow

respectively.Fig.7 shows that the spectra of green band in ZnSe:Cu crystals do not shift with decay time.It indicates that the recombination process of the green band ascribes to non D-A pair transition.According to above results

it may be considered that the deep acceptor level of E

v

+0.30eV obtained in ODLTS spectrum should be attributed to the acceptor related to Cu-G center.