M. Udhayasankar

On the Analysis of Hydrogen in as grown and Ion Implanted GaAs Single Crystals

Hydrogen detection and analysis was carried out on the undoped vsemi-insulating (S.I.) gallium arsenide (GaAs) single crystal using conventional elastic recoil detection analysis (ERDA) technique with high energy, heavy ion beam. Presence of hydrogen (nearly 3 x 10 20 atoms/cc) has been observed on the as-grown samples and further high concentration of atomic hydrogen (total concentration of 7 x 10 20 atoms/cc) was found at the surface and was found to be decreasing with depth after 100 nm. Further the low energy hydrogen and oxygen ions implanted separately in GaAs at room temperature were also analysed by ERDA technique. From the analysis, the projected range (R p ) of 100 keV hydrogen and oxygen ions in GaAs was determined to be 891 nm (with ΔR equal to 320 nm), 170 nm (with AR equal to 120 nm) respectively. The experimentally determined values of both R and ΔR are more as compared with the values obtained using the TRIM theoretical program. Low temperature (4K) photoluminescence (PL) measurements of un-implanted and H + implanted samples show the passivation of intrinsic deep level defect EL2 and shallow acceptor impurity carbon by the low energy implanted hydrogen ions. The low energy hydrogen implantation may be used as a method of hydrogenation for passivation.

Electrical characteristics of 100 MeV 28Si implanted LEC grown GaAs〈100〉

Abstract Undoped semi-insulating gallium arsenide single crystals were grown in pBN crucible using LEC technique. 28Si implantation at various fluences was carried out using 100 MeV 28Si ion. Implanted samples were characterised using four probe and Hall measurements. In-situ resistance measurements were carried out for samples implanted with various fluences. The electrical characterisation results of 100 MeV 28Si implanted GaAs samples show an increase in mobility 5774 cm2/V.s (3800 cm2/V.s) and a decrease in sheet resistivity of the order of 2 × 10 2 Ω/q . The increase in mobility at 300 K may be due to better electrical homogeneity in the implanted layer, than in the virgin substrate. The implanted samples ( 100 MeV 1.5 × 10 13 cm −2 ) were annealed at different temperatures in the range of 200–400°C and characterised using Hall measurements at different temperatures (300–380 K). The implantation profile of the two buried layers by 100 MeV 1 × 10 12 cm −2 and 80 MeV 1 × 10 12 cm −2 for 28Si ion were observed and analysed using Scanning Electron Microscopy.

Investigations of beryllium in CBE grown epitaxial layers and profiling of multilayers by electro-chemical C–V measurements

Abstract Profiling of p-type dopant in low band gap materials such as indium gallium arsenide (InGaAs) and indium phosphide (InP) were carried out using a computer controlled electro-chemical carrier profiling system. The electrically active carrier concentration of beryllium (Be), a widely used p-type dopant, has been investigated in the chemical beam epitaxially (CBE) grown InP and InGaAs layers. At very high Be doping, the surface roughness and the formation of Be precipitates on the growing InP or ternary surface seems to influence the electro-chemical capacitance–voltage (ECV) profiling of Be dopant. The profiling of heavy Be dopant is limited by the surface degradation of the epilayers. The ECV measurements combined with the stylus profiler measurements further show the abruptness of the growth interface and it confirms the interface control of the grown epi-materials. We also show the complete profiling of a multilayer structure grown by the CBE technique for opto-electronic and photonic applications.

Effect of irradiation on the microhardness of the LEC grown semi-insulating GaAs single crystals

Abstract Undoped semi-insulating (SI) gallium arsenide (GaAs) single crystals were grown in the 〈100〉 direction by the liquid encapsulated Czochralski (LEC) technique. The grown crystals were cut and characterised by Hall effect measurement in the Van der Pauw configuration. Ion implantation has profound effects upon the elastic, mechanical, optical and structural properties of semi-conducting materials. The present study deals with the effect of ion implantation on microhardness of GaAs. Hydrogen ion implantation was carried out at room temperature on GaAs samples at 100 keV energy. Microhardness measurements were carried out after implantation and the change in the microhardness as a function of ion dose was evaluated. The irradiated samples were also characterised by using X-Ray diffraction (XRD) techniques.

Investigations on Au, Ag, and Al Schottky diodes on liquid encapsulated Czochralski grown n-GaAs(100)

The Schottky barrier heights of metals Au, Ag, and Al fabricated by vacuum vapor deposition on liquid encapsulated Czochralski (LEC) grown undoped ntype GaAs (n = 2.35 × 1015 cm−3) were measured with current-voltage (I-V) and capacitance-voltage (C-V) techniques. Good ohmic contacts were obtained through an after deposition anneal at 430°C for two minutes in an argon gas atmosphere. In the as-deposited state, Au, Ag, and Al gave very similar I-V characteristics for n-type substrates with the barrier height qϕb = 0.81-1.16 eV and ideality factor n = 1.02-1.15. The C-V measurement also gives the same value of barrier height. The distribution of carrier concentration along the radial distance of the wafer is of‘M’ shape. The Al/GaAs interfaces give the nonideal rectification behavior. The Au/GaAs interfaces give the near ideal rectification behavior. The barrier height of this interface is 0.89-0.92 eV and the ideality factor is about 1.10–1.19. Electron traps in the wafer have been found by constant capacitance deep level transient spectroscopy (CC-DLTS). Mainly the EL2, EL6, and EL3 (EI1) trap levels are prominent.

On the development of an electrolyte for ECV profiling of AlInAs

AlInAs layers latticed matched to InP are important for the fabrication of high speed electronic and opto electronic devices. In this work, we present the realisation of three different electrolytes for ECV measurements of AlInAs. A comparison with the behaviours of the different electrolytic solutions has been discussed. Among the new electrolytic solutions, 1HNO/sub 3/:20H/sub 2/O::1HF:25H/sub 2/O and NH/sub 4/F (0.75M) solutions were suitable for ECV profiling of AlInAs. They have low electrolytic resistance and free chemical etch rate values with good Schottky barrier characteristics. They are able to distinguish between n-type and p-type carriers and the variation in their concentration levels in addition to compatibility with the InP substrate material. But during profiling, formation of flakes has been noticed as the junction was approached. ECV estimated carrier concentration values and expected values agree, but the ECV measured thickness values do not agree well with the stylus profiler measured thickness values. Although these electrolytic solutions may be useful in principle for profiling of AlInAs/InP structures, further experiments are required to understand the mechanism of the dissolution of AlInAs thereby completely realising an electrolyte for a successful ECV profiling of AlInAs.