Thin heavily Mg-doped InGaN and GaN compound contact layer is used to form Ni/Au Ohmic contact to p-GaN. The growth conditions of the compound contact layer and its effect on the performance of Ni/Au Ohmic contact to p-GaN are investigated. It is confirmed that the specific contact resistivity can be lowered nearly two orders by optimizing the growth conditions of compound contact layer. When the flow rate ratio between Mg and Ga gas sources of p＋＋-InGaN layer is 10.6% and the thickness of p＋＋-InGaN layer is 3 nm, the lowest specific contact resistivity of 3.98× 10-5 Ω cm2 is achieved. In addition, the experimental results indicate that the specific contact resistivity can be further lowered to 1.07 × 10-7Ω.cm2 by optimizing the alloying annealing temperature to 520 ℃.
Two series of p-GaN films grown at different temperatures are obtained by metal organic chemical vapor deposition（MOCVD）. And the different variation behaviors of resistivity with growth condition for high- temperature（HT）-grown and low-temperature（LT）-grown p-GaN films are investigated. It is found that the resistivity of HT-grown p-GaN film is nearly unchanged when the NH_3 flow rate or reactor pressure increases. However, it decreases largely for LT-grown p-GaN film.These different variations may be attributed to the fact that carbon impurities are easy to incorporate into p-GaN film when the growth temperature is low. It results in a relatively high carbon concentration in LT-grown p-GaN film compared with HT-grown one. Therefore, carbon concentration is more sensitive to the growth condition in these samples, ultimately,leading to the different variation behaviors of resistivity for HT- and LT-grown ones.
The influence of a deep-level-defect（DLD） band formed in a heavily Mg-doped GaN contact layer on the performance of Ni/Au contact to p-GaN is investigated. The thin heavily Mg-doped GaN（p^＋＋-GaN） contact layer with DLD band can effectively improve the performance of Ni/Au ohmic contact to p-GaN. The temperature-dependent I–V measurement shows that the variable-range hopping（VRH） transportation through the DLD band plays a dominant role in the ohmic contact. The thickness and Mg/Ga flow ratio of p^＋＋-GaN contact layer have a significant effect on ohmic contact by controlling the Mg impurity doping and the formation of a proper DLD band. When the thickness of the p^＋＋-GaN contact layer is 25 nm thick and the Mg/Ga flow rate ratio is 10.29%, an ohmic contact with low specific contact resistivity of 6.97×10^-4Ω·cm^2 is achieved.
InGaN/GaN p-i-n solar cells, each with an undoped In0.12Ga0.88N absorption layer, are grown on c-plane sapphire substrates by metal-organic chemical vapor deposition. The effects of the thickness and dislocation density of the absorp- tion layer on the collection efficiency of InGaN-based solar cells are analyzed, and the experimental results demonstrate that the thickness of the InGaN layer and the dislocation density significantly affect the performance. An optimized InGaN- based solar cell with a peak external quantum efficiency of 57% at a wavelength of 371 nm is reported. The full width at half maximum of the rocking curve of the （0002） InGaN layer is 180 arcsec.
Models for calculating the sheet densities of two-dimensional electron gas （2DEG） induced by spontaneous and piezoelectric polarization in A1GaN/GaN, A1GaN/A1N/GaN, and GaN/A1GaN/GaN heterostructures are provided. The detailed derivation process of the expression of 2DEG sheet density is given. A longstanding confusion in a very widely cited formula is pointed out and its correct expression is analyzed in detail.
Electron leakage still needs to be solved for In Ga N-based blue-violet laser diodes（LDs）, despite the presence of the electron blocking layer（EBL）. To reduce further electron leakage, a new structure of In Ga N-based LDs with an In Ga N interlayer between the EBL and p-type waveguide layer is designed. The optical and electrical characteristics of these LDs are simulated, and it is found that the adjusted energy band profile in the new structure can improve carrier injection and enhance the effective energy barrier against electron leakage when the In composition of the In Ga N interlayer is properly chosen. As a result, the device performances of the LDs are improved.
Electron leakage in GaAs-based separately confined heterostructure 808 nm laser diodes （SCH LDs） has a serious influence on device performance. Here, in order to reduce the energy of electrons injected into the quantum well （QW）, an A1GaAs interlayer with a smaller A1 component is added between the active region and the n-side waveguide. Numerical device simulation reveals that when the Al-composition of the A1GaAs interlayer and its thickness are properly elected, the electron leakage is remarkably depressed and the characteristics of LDs are improved, owing to the reduction of injected electron energy and the improvement of QW capture efficiency.
The influences of polarization and p-region doping concentration on the photocurrent response of Al0.4Ga0.6N/Al0.4Ga0.6N /Al0.65Ga0.35N p-i-n avalanche photodetector are studied in a wide range of reverse bias voltages. The simulation results indicate that the photocurrent under high inverse bias voltage decreases with the increase of polarization effect, but increases rapidly with the increase of effective doping concentration in p-type region. These phenomena are analyzed based on the calculations of the intensity and distribution of the electric field. A high p-region doping concentration in the p-i-n avalanche photodetector is detrimental polarization-induced electrostatic field. shown to be important for the efficient compensation for the
