| 1. |
- Chen, Weimin, 1959-, et al.
(författare)
-
Optical and Microwave Double Resonance of III-nitrides
- 1999
-
Ingår i: Joint International Meeting the 196th Meeting of The Electrochemical Society ECS and the 1999 Fall Meeting of The Electrochemical Society of Japan ECSJ,1999. ; , s. 764-
-
Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
|
|
| 2. |
- Buyanova, Irina, 1960-, et al.
(författare)
-
Effect of electron irradiation on optical properties of gallium nitride
- 1999
-
Ingår i: Physica Scripta. - 0031-8949 .- 1402-4896. ; T79, s. 72-75
-
Tidskriftsartikel (refereegranskat)abstract
- The effect of electron irradiation on the optical properties of GaN epilayers is studied in detail by photoluminescence (PL) spectroscopy. The most common types of GaN material are used, i.e. strained heteroepitaxial layers grown on 6H SiC or Al2O3 substrates, and thick bulk-like layers with the conductivity varying from n-type to semi-insulating and p-type. The main effects of electron irradiation on all investigated samples are found to be as follows: (i) a radiation-induced quenching of excitonic emissions in the near band gap region; (ii) an appearance of broad overlapping PL emissions within the spectral range 0.7-1.1 eV and (iii) the appearance of a PL band with a sharp no-phonon (NP) line at around 0.88 eV followed by a rich phonon assisted sideband. The 0.88 eV band is shown to originate from an internal transition of a deep defect. With increasing temperature a hot PL line can be observed at about 2-4 meV above the NP line, originating from higher lying excited states of the defect. The electronic structure of the 0.88 eV defect is shown to be very sensitive to the internal strain field in the GaN epilayers.
|
|
| 3. |
- Buyanova, Irina, 1960-, et al.
(författare)
-
Electronic structure of the 0.88-eV luminescence center in electron-irradiated gallium nitride
- 1999
-
Ingår i: Physical review. B, Condensed matter and materials physics. ; 60:3, s. 1746-1751
-
Tidskriftsartikel (refereegranskat)abstract
- Photoluminescence (PL) spectroscopy is employed to determine the nature of a near-infrared PL emission with a no-phonon line at ∼0.88 eV, commonly present in electron-irradiated GaN. This PL emission is suggested to originate from an internal transition between a moderately shallow excited state (with an ionization energy ∼21 meV) and the deep ground state (with an ionization energy ∼900 meV) of a deep defect. The existence of a higher-lying second excited state related to the 0.88-eV PL center is also shown from temperature-dependent studies. A different electronic character of the wave functions related to the first and second excited states has been revealed by PL polarization measurements. Since the PL emission has been observed with comparable intensity in all electron-irradiated GaN samples independent of doping on the starting material, it is proposed that either native defects, or common residual contaminants or their complexes are involved. The substitutional ON donor (or related complex) is considered as the most probable candidate, based on the observed striking similarity in the local vibrational properties between the 0.88-eV PL centers and the substitutional OP donor in GaP.
|
|
| 4. |
|
|
| 5. |
- Chen, Weimin, 1959-, et al.
(författare)
-
Role of the Substitutional Oxygen Donor in the Residual n-type Conductivity in GaN
- 1999
-
Konferensbidrag (refereegranskat)abstract
- A detailed photoluminescence (PL) study reveals a striking similarity in local vibrational properties of a defect center in GaN as compared to that for the substitutional OP donor in GaP. This observation could be interpreted as if the center is in fact related to the substitutional oxygen donor in GaN. The deep-level nature experimentally determined for the defect center calls for caution of a commonly referred model that the substitutional oxygen donor is responsible for the residual n-type conductivity in GaN.
|
|
| 6. |
|
|
| 7. |
- Monemar, Bo, et al.
(författare)
-
Radiative recombination in In0.15Ga0.85N/GaN multiple quantum well structures
- 1999
-
Ingår i: MRS Internet Journal of Nitride Semiconductor Research. - 1092-5783. ; 4:16
-
Tidskriftsartikel (refereegranskat)abstract
- We present a study of the radiative recombination in In0.15Ga0.85N/GaN multiple quantum well samples, where the conditions of growth of the InGaN quantum layers were varied in terms of growth temperature (< 800 degrees C) and donor doping. The photoluminescence peak position varies strongly (over a range as large as 0.3 eV) with delay time after pulsed excitation, but also with donor doping and with excitation intensity. The peak position is mainly determined by the Stark effect induced by the piezoelectric field. In addition potential fluctuations, originating from segregation effects in the InGaN material, from interface roughness, and the strain fluctuations related to these phenomena, play an important role, and largely determine the width of the emission. These potential fluctuations may be as large as 0.2 eV in the present samples, and appear to be important for all studied growth temperatures for the InGaN layers. Screening effects from donor electrons and excited electron-hole pairs are important, and account for a large part of the spectral shift with donor doping (an upward shift of the photoluminescence peak up to 0.2 eV is observed for a Si donor density of 2 x 10(18) cm(-3) in the well), with excitation intensity and with delay time after pulsed excitation (also shifts up to 0.2 eV). We suggest a two-dimensional model for electron- and donor screening in this case, which is in reasonable agreement with the observed data, if rather strong localization potentials of short range (of the order 100 Angstrom) are present. The possibility that excitons as well as shallow donors are impact ionized by electrons in the rather strong lateral potential fluctuations present at this In composition is discussed.
|
|
| 8. |
|
|
| 9. |
|
|
| 10. |
|
|
