M. Kuttler

4d- and 5d-transition metal acceptor doping of InP

We present a detailed study of the electrical activation of the 4d- and 5d-transition metals Ru, Rh, Os and Ir in InP. The layers investigated were grown by metalorganic chemical vapor deposition and investigated by secondary ion mass spectroscopy and deep level transient spectroscopy. We show that InP doping with these transition metals is possible up to concentrations above 10 18 cm -3 without any formation of macroscopic precipitates. All of these transition metals offer a low diffusivity and induce deep levels in InP. Deep levels close to the middle of the bandgap are observed for Rh and Ru doping, making them interesting candidates to turn InP semi-insulating. The transition-metal-related deep level concentrations achieved so far are well above 10 15 cm -3 . The electrically active concentration of these transition metals is strongly dependent on their particular reactivity, especially with hydrogen, and ranges between 0.1% for Rh and 5% for Os. In the case of Rh doping the electrically active concentration can be enhanced by a factor of 5 using nitrogen carrier gas instead of hydrogen.

Novel results on compensation processes in ZnSe:N

Abstract Compensation in ZnSe:N was investigated. The total nitrogen concentration in the samples was determined by two different techniques: secondary ion mass spectroscopy and nuclear reaction 15 N(p, αγ) 12 C analysis. The net free hole concentration N A − N D was correlated with these results. A ratio of (N A − N D ) [ N ] up to 50% was observed. Furthermore, we studied the excitonic region of the photoluminescence of ZnSe:N. Two different transitions correlated with nitrogen complexes could be observed. In lightly doped ZnSe:N a donor like complex was observed, while in highly doped an acceptor like complex dominates. The origin of these complexes is discussed.

Thermal stability of the midgap acceptor rhodium in indium phosphide

We investigated the thermally induced redistribution of Rh in low pressure MOCVD grown InP structures by means of secondary‐ion‐mass‐spectroscopy. Analogous measurements for InP:Fe structures serve as reference. On alternately Rh‐doped/undoped InP structures an upper limit for the diffusion coefficient of DRh(800u2009°C)≤1×10−14 cm2/s is established much smaller than DFe(750u2009°C)=1×10−11 cm2/s. No exchange reactions are observed at the interface of p‐InP/InP:Rh structures. Only Rh implanted into InP shows defect induced redistribution into amorphous areas. Rh is superior to Fe as far as thermal stability is concerned.

Lateral index guiding in ZnCdSe quantum well lasers by selective implantation-induced disordering

Local implantation-induced disordering of ZnCdSe quantum wells is applied to generate lateral index guided II–VI lasers. Lateral selectivity of implanted nitrogen ions is achieved by metal stripes also used for contacts. Secondary ion mass spectroscopy and luminescence prove that quantum well intermixing can be generated without subsequent thermal treatment. Lateral index guiding in II–VI lasers after implantation is demonstrated by recording the near-field pattern, yielding a lateral index step of the order of 10−3. First full index-guided injection lasers with an implantation-induced lateral confinement are processed. Threshold current density is reduced by 40% and emission characteristics of these lasers are strongly improved.

Doping-dependent Mg diffusion in ZnMgSSe/ZnSSe-structures

Diffusion of magnesium in ZnMgSSe/ZnSSe-structures is investigated. The superlattices structures is partly implanted and annealed. Annealing atmosphere, time and temperature are varied. Secondary-ion mass spectroscopy investigations demonstrate that magnesium diffuses via group II lattice sites. Diffusion enhancement results for p-type doping as well as additional group II vacancy generation. Diffusion coefficients for the different annealing and doping conditions are determined.

Diffusion induced disordering (DID) in ZnSSeZnSe superlattices

Thermally induced disordering of ZnSSe/ZnSe superlattices was studied by X-ray diffraction, secondary-ion-mass-spectroscopy and cathodoluminescence. The structures were grown by MOVPE and annealed in H 2- or Se-atmosphere. The superlattices are found to be stable up to 750°C in H 2 -atmosphere whereas a heat treatment in Se-atmosphere at 590°C leads to a complete intermixing. A Si 3 N 4 cap was used to protect the superlattice from the Se-atmosphere and to achieve a laterally structured intermixing of the superlattice. The effect of lateral intermixing is demonstrated by spatially resolved cathodoluminescence.

Novel ways to grow thermally stable semi-insulating InP-based layers

Abstract Semi-insulating InP is generally grown by Fe doping. In contact with p-type layers, however, semi-insulating characteristics turn out to be difficult to reproduce because of pronounced interdiffusion of Fe and p-type dopants. Co-doping of InP:Fe with Ti is shown to be a universal process for the preparation of thermally stable high-resistivity layers. Fe + Ti co-doping can compensate both excess shallow donors and excess shallow acceptors up to concentrations of 8 × 10 16 and 2 × 10 16 cm -3 , respectively. In contrast to InP:Fe, resistivities in excess of 10 7 Ω cm are obtained in contact with both symmetric n- and p-type current injecting contacts. Moreover, co-doping of semi-insulating InP:Fe with Ti is found to suppress the interdiffusion of Fe and p-type dopants. Therefore, the out-diffusion and accumulation of Fe in other regions of complex device structures can be significantly reduced. A comprehensive model accounting for these phenomena is presented. A totally different way to produce thermally more stable semi-insulating InP layers is to replace Fe by a less diffusive deep acceptor. We propose the 4d transition metal Rh as a potential alternative. The diffusion of Rh is shown to be practically nonexistent and near-midgap Rh levels are found by means of DLTS in InP at E v + 730 meV and in InGaAs at E c - 380 meV below the conduction band. We conclude these levels to be the single acceptor states of Rh substitutionally incorporated on cation sites.

Ion implantation of zirconium and hafnium in InP and GaAs

Abstract The redistribution of Zr and Hf implanted into InP and GaAs and the lattice recrystallization after annealing are studied. Zr and Hf profiles are measured by secondary ion mass spectroscopy. The recryslallization is evaluated by Rutherford backscattering/ channeling and X-ray double crystal diffractometry. After low dose implantation, both Zr and Hf show absolute thermal stability under standard heat treatments. Only after high dose implantation Zr is found to accumulate below the surface and to diffuse slowly into the bulk of InP and GaAs samples with a more pronounced redistribution in InP than in GaAs. Hafnium, in contrast, proves to be thermally stable even under extreme implantation and annealing conditions. A novel Zr-related level with an activation energy of (0.53±0.03) eV is identified in Zr doped n-InP:Si by deep level transient spectroscopy.

Stability issues of quaternary CdZnSSe and ternary CdZnSe quantum wells in blue—green laser diodes

Abstract Thermally induced Cd diffusion in CdZn(S)Se/Zn(S)Se multi-quantum well-structures has been investigated in order to study point defects and their generation in II–VI/III–V heterostructures and to find a thermally stable quantum well design. Samples were annealed in Zn atmosphere and diffusion coefficients were determined with secondary ion mass spectroscopy. Cd diffusion coefficients as low as 1.2 × 10 −18 cm 2 /s at T = 575°C were found in a CdZnSSe/ZnSSe structure. Samples annealed in Zn atmosphere indicate a higher stability of CdZnSSe than of CdZnSe, but samples annealed in N 2 seem to show the opposite tendency. Laser diodes show low threshold current densities of 400 A/cm 2 for both kinds of wells.

Efficient lateral index guiding of II–VI laser structures by implantation-induced disordering

Abstract Implantation-induced disordering in ZnCdSe-based quantum wells and superlattices is investigated and used to generate lateral index-guided laser structures. The structures are implanted with Nitrogen at doses of 1 × 10 15 4 × 10 15 cm −2 at energies ranging between 110 and 230 keV and subsequently annealed at temperatures up to 460°C in Zn-atmosphere. Distinct intermixing is identified by secondary-ion-mass-spectroscopy. Lateral selective implantation is performed by using stripe masks 5–30 μm wide. Lateral selectivity is proven by cathodoluminescence. Waveguiding of selectively implanted superlattices and laser structures is demonstrated by recording the near-field pattern. The implanted structures exhibit index guiding with and without subsequent annealing, demonstrating that index guiding is already achieved by the weak intermixing induced by implantation.