Effect of Hydrogenation on the Photoluminescence Properties of p-type InP.

We report on the effect of hydrogenation on the low temperature photoluminescence properties of Cd or Zn doped p-type InP. The samples consisted of Cd-diffused layers on n-type (n wig 5 times 10 sup 17 cm sup -3) substrates or Zn doped p-type (p wig 3 times 10 sup 18 cm sup -3) substrates. In the former sample the carrier concentration and diffusion depths are wig 2.5 times 10 sup 18 cm sup -3 and 2.1 +- 0.1 mum, respectively. The low temperature (5.5K) photoluminescence (PL) spectrum of the as-grown InP:Zn sample shows a Zn sub In acceptor related transition near the band edge at 1.386 eV and a Zn related PL band at 1.214 eV and a phosphorus vacancy V sub p related PL band at 1.01 eV. The PL spectrum of the Cd- diffused InP sample consists of the free electron-to-Cd sub In acceptor transition at 1.368 eV and a Cd-related deep center luminescence band at wig 1.28 eV. After hydrogenation of the samples by exposure to hydrogen plasma through an H-permeable surface protective coating at 250 degree C for 30 min, which completely passivates the Cd sub In or Zn sub In acceptors over a depth of more than a micron, the deep luminescence bands disappeared with a concomitant increase in the intensity of the near band edge emission. In the case of InP:Zn, a wig 2000 fold increase in intensity was observed, while in the case of InP:Cd, a wig 30 fold increase was observed. Such large increases in radiative efficiency together with the elimination of the deep luminescence bands indicate hydrogen passivation of deep non-radiative centers in addition to passivation of shallow electrically active centers. The larger increase in PL intensity of the Zn doped InP sample is due to a higher concentration of non-radiative centers in it compared to the Cd-diffused sample, as evidenced by the presence in the unhydrogenated condition of the V sub p related band in the former (and its very low initial PL efficiency) and not in the latter. After hydrogenation the 1.386 eV band in InP:Zn and the 1.368 eV band in InP:Cd were replaced by a band at 1.36 eV. This band is attributed to new radiative centers created solely by hydrogenation. Rapid thermal annealing of the hydrogenated samples at 325 degree C/30 sec, nullifies the improvement in the radiative efficiency of the Zn doped sample and recovers the deep center emission bands as well as the 1.386 eV band. On the other hand, in the Cd-diffused sample the improvement in the radiative efficiency due to hydrogenation is retained even up to 425 degree suggesting increased thermal stability of hydrogen passivated deep non- radiative centers. Further, neither the 1.368 eV nor the 1.28 eV luminescence bands are restored. Instead, the higher annealing temperature gave rise to new emission bands near the band edge.