Masahito Migita

p‐type conductivity control of ZnSe highly doped with nitrogen by metalorganic molecular beam epitaxy

p‐type ZnSe with resistivity low enough for device application has been realized by metalorganic molecular beam epitaxy. This method has enabled growth of p‐type ZnSe doped with nitrogen at concentrations as high as 1019 cm−3 by using ammonia as a dopant source. The dependence of photoluminescence and electrical properties on substrate temperature has been investigated. Hall measurements show p‐type conductivity with a resistivity of 0.57 Ω cm, a carrier concentration of 5.6×1017  cm−3, and a Hall mobility of 20 cm2/V s.

ZnSe p‐n junctions produced by metalorganic molecular‐beam epitaxy

The p‐n junction in nitrogen‐doped p‐type ZnSe/undoped n‐type ZnSe on n‐type GaAs (100) is successfully produced by metalorganic molecular‐beam epitaxy. p‐type conduction of ZnSe is achieved as a consequence of high nitrogen doping (5×1018–1×1019 cm−3). The data points of C−2 (C: capacitance) against voltage of the p‐n junction are approximated by a straight line and the diffusion potential estimated from the plots is about 2.4 eV. Electron‐beam‐induced current also directly demonstrates the formation of a ZnSe p–n junction. Furthermore, blue emission is observed from the 5‐V foward‐biased ZnSe p‐n junction at 77 K.

p-Type conduction of ZnSe highly doped with nitrogen by metalorganic molecular beam epitaxy

Abstract Highly conductive p-type ZnSe layers have been grown reproducibly as a consequence of high nitrogen-doping (≈1019cm-3) by using metalorganic molecular beam epitaxy (MOMBE). The dependence of electrical and photoluminescent properties on substrate temperature (Ts) has been investigated. p-Type conductivity of the ZnSe films at room temperature is enhanced with an increase in Ts; e.g. from a high 0.1 MΩcm resistivity at Ts=300°C to a low 0.57 Ωcm resistivity at 450 °C. By contrast, the dependence of the electrical properties for undoped ZnSe on Ts is similar to that of nitrogen-doped ZnSe except for the type of conductivity. The n-type resistivity of undoped ZnSe also decreases with an increase in Ts (e.g. 20 KΩcm at 300°C to 3.5 Ωcm at 400°C). A nitrogen-doped p-type ZnSe/undoped n-type ZnSe junction grown at 350°C on n-GaAs (100) has been succesfully produced. The diffusion potential of the p-n junction can be evaluated to be between 2.45 and 2.55 eV from the C-2-V plot. Observations of electron beam induced current (EBIC) have also shown formation of the p-n junction. At 77 K bluish emission has been observed from the p-n junction with a 5V forward-bias voltage.

The preparation of ZnS:Mn electroluminescent layers by MOCVD using new manganese sources

In the preparation of ZnS:Mn polycrystalline films by MOCVD, CPM [(C5H5)2Mn: di-π-cyclopentadienyl manganese] and BCPM [(CH3C5H4)2Mn: bismethylcyclopentadienyl manganese] are employed as new doping sources, and are compared with previously reported TCM [(CH3C5H4)Mn(CO)3: tricarbonyl methylcyclopentadienyl manganese]. In contrast to TCM, which is only partially decomposed even at 400 ∼ 500°C, CPM and BCPM are completely decomposed around the optimum growth temperature of ZnS, i.e. 280–350°C. When thermally decomposed, TCM produces a by-product containing Mn and carbonyl, which does not contribute to the luminescence, but CPM and BCPM do not. By these advantages, the double-insulator type electroluminescent (EL) devices prepared with CPM or BCPM show higher luminance than those prepared with TCM. A 500 nm thick ZnS:Mn layer by CPM gives the maximum efficiency (ηmax) of 4.8 lm/W and a saturated luminance (Lsat) of 4300 cd/m2 at 1 kHz sine wave excitation. By BCPM, Lsat of 3150 cd/m2 was obtained. Meanwhile, the devices prepared with TCM in this investigation show Lsat to be less than 1000 cd/m2 and a low efficiency of less than 1 lm/W. By the combination with red filters, ZnS:Mn by MOCVD with CPM or BCPM can also provide efficient red EL. When a glass filter (the cut-off wavelength is 590 nm) is used, the EL device prepared with CPM gives Lsat=1420 cd/m2 and ηmax=1.6 lm/W (the color coordinates, x=0.626 and y=0.373) at 1 kHz sine wave excitation.

Luminescence properties of ZnS/GaAs grown by gas source MBE

Abstract High purity cubic ZnS films were grown on GaAs(100) by the gas source MBE method using (CH 3 ) 2 Zn and H 2 S as source materials. Photoluminescence studies of these films by the excitation of an N 2 or an Xe-Cl excimer laser have shown that the intensity of self-activated emission depends on the [S]/[Zn] ratio and the substrate temperature. No SA emission was observed for ZnS films grown at 400 °C or more with an [S]/[Zn] ratio of 2.3. Band edge emission consists of four sharp lines. The one at the highest photon energy, 3.797 eV, can be assigned to the recombination of a free exciton.

n-Type and p-type conductivity control of ZnSe grown by metalorganic molecular beam epitaxy using methyliodide and ammonia

Abstract Electrical properties of ZnSe heavily doped with iodine or nitrogen have been investigated. The film crystals of ZnSe were grown by metalorganic beam epitaxy with methyliodide or ammonia as a dopant source. Iodine doping provides highly conductive n-type ZnSe with resistivity as low as 0.02 Ω cm and a carrier concentration of 2.2×10 18 cm −3 at room temperature. For ZnSe:N, ohmic electrodes have been formed with gold by annealing at 360°C for 5 min in N 2 atmosphere. The activation energy of p-type conductivity, E A , is 90–110 meV when the growth temperature ( T g ) is 350°C, while ( E A is 80–100 meV when T g =400° C . The acceptor concentration N A decreases from 9×10 16 −3×10 17 to 3×10 16 −7X10 16 cm −3 as T g is elevated from 350 to 400°C. However, the difference between the acceptor and residual donor concentration ( N A − N D ) is about 5 times larger for 400°C than for 350°C. N A − N D is 4×10 15 −7×10 15 cm −3 for 350°C and 2×10 16 −4×10 16 cm −3 for 400°C. This result indicates that electrical properties of the p-type ZnSe:N are improved as T g increases. Photoluminescence properties of n-ZnSe:I and p-ZnSe:N are also reported.

Formation of pyrene crystalline thin films assisted by helium ion bombardment

This paper reports on the effect of low energy He+ ion‐beam bombardment upon the structure of pyrene thin films formed on quartz substrates. Films are prepared by vacuum evaporation during ion bombardment at room temperature. The structure of the film is controlled by the kinetic energy and current density of the ions. The colorless and transparent crystalline films preferentially oriented with their {001} plane parallel to the substrates are obtained by bombardment of 350 to 500 eV, 60 nA/cm2 He+ ions. Ion‐beam irradiation of the higher ion current density enhances intermolecular chemical reactions and, as a result, a crystalline polymer with its {001} plane parallel to the substrate is produced.

Blue-green light-emitting diodes with p-ZnSSe highly doped with nitrogen grown by metalorganic molecular beam epitaxy and molecular beam epitaxy

Abstract The p-type doping of ZnSSe grown by MOMBE (metalorganic molecular beam epitaxy) and MBE (molecular beam epitaxy) has been comparatively studied. The p-type doping by using ammonia as a dopant source in MOMBE resulted in p-ZnSe with hole concentration of up to 10 17 cm -3 . Perfect ohmic contact characteristics were achieved by MOMBE for Au/p-ZnSe:N with hole concentration of 5.5 × 10 17 cm -3 . On the other hand, p-type doping in MBE by using nitrogen plasma as a dopant resulted in p-ZnSe with net acceptor concentration of up to 7.6 × 10 17 cm -3 . I–V characteristics with the lowest Schottky barriers were obtained for Au/p-ZnSe with net acceptor concentration of 6.6 × 10 16 to 7.6 × 10 17 cm -3 for ZnSe:N and of 2.8 × 10 16 to 1.2 × 10 17 cm -3 for ZnS x Se 1− x :N ( x = 0.03−0.12). The characteristics of ZnSe light emitting diodes with p-ZnSe grown by using ammonia in MOMBE are described. The characteristics of a ZnCdSe/ZnSSe laser diode with p-ZnSSe grown by using nitrogen plasma in MBE are discussed.

Efficient ZnS:Mn Electroluminescent Films Grown by Metal Organic Chemical Vapor Deposition

Electroluminescent ZnS:Mn films grown by reduced pressure MOCVD are characterized in comparison with films deposited by the EB method. An important feature of the crystallinity is that the mean grain size as observed by X-ray diffraction line widths and by TEM images is larger in the MOCVD films than in the EB films. The intensities of PL and EL reach their maximum at Mn concentrations from 0.8 to 1.0 wt%, which is considerably higher than that for EB deposition (0.5 wt%). The MOCVD technique can provide about twice the EL efficiency as the EB method. This can be ascribed to the large grain size and the uniform Mn distribution.