Xiawan Wu

Hydrogen neutralization effect in bulk N-type LEC InP materials

Abstract FTIR spectroscopy measurements indicate a presence of high concentration hydrogen existing in the liquid encapsulated Czochralski grown undoped InP wafers. These undoped InP can be annealed to be semi-insulating (SI) reproducibly. Hydrogen can facilitate the formation of anti-site defects in InP and can also induce electrically-active hydrogen related defects. The annealed behavior of InP is proved possible to be originated from the neutralization effect of hydrogen that is supplied by the dissociation of hydrogen complexes in the process of annealing. The process of hydrogen passivation of donors is discussed. Besides neutralizing impurities and defects in InP, hydrogen induces new hydrogen related defects in the band gap, and can also activate the formation of complexes involving P In , so it plays an important role in the charge compensation process in SI InP obtained by high temperature annealing.

Synthesis of indium phosphide polycrystalline

A large quantity of high purity InP crystal material has been produced by the phosphorus in-situ injection synthesis. In the injection method, phosphorus reacts with indium very quickly so that the rapid polycrystalline synthesis is possible. The injection speed, melt temperature, phosphorus excess, and so on are also important for a successful synthesis process. About 3200-4800 g stoichiometric high purity poly InP is synthesized reproducibly by improved P-injection method in the high-pressure puller. Twin-Free InP single crystals with diameter of 50-110 mm can be pulled after the synthesis. In the present work, the characterization of InP polycrystalline was studied by van der Pauw method, GDMS, and PL.

Character of non-stoichiometric InP bulk crystal

P-rich, In-rich and stoichiometric undoped InP melts have been synthesized by phosphorus in-situ injection method, InP crystal ingots have been grown from these melts by LEC method. The difference in these InP crystal should be attributed to the change of stoichiometry. Some samples from these ingots have been characterized by the Hall effect and Fourier transform infrared (FT-IR) spectroscopy measurements respectively. The Hall effect measurement results indicate that the carrier concentration of P-rich undoped InP is higher than that of In-rich and stoichiometric undoped InP materials. The intensive absorption peaks indicate that our phosphorus in-situ injection synthesis LEC undoped InP materials have relatively high concentration of hydrogen related complexes. The FT-IR results are also in agreement with the carrier concentration of InP grown from different stoichiometric melts.

Homogeneity study of wafers of InP single crystal grown from P-rich melt

A 4-inch InP single crystal has been grown from P-rich melt by the P-injection synthesis LEC method. Due to the non-stoichiometric condition, there are many pores in the tail of the ingot. The wafers cut from it are experimented by means of PL mapping and EPD mapping. The PL peak intensity standard deviation of the 4-inch InP wafer is higher. The EPDs around the pores are larger than the other regions. Besides the stress releasing, the pores and the high concentration of dislocations around them presents the leading factors causing the inhomogeneity of the wafer. We have explained the phenomena.

Large diameter Sn-doped indium phosphide single crystal growth by LEC method

Sn-doped InP is being used as a platform for a wide variety of fiber communications components, including lasers, LEDs, semiconductor optical amplifiers, modulators and photo-detectors. The more the diameter is, the more imperfection of the InP crystal would be. The substrates with large diameter are desired in order to realize low devices cost. In recent years, we have developed a high quality 3-inch and 4-inch Sn-doped InP single crystal growth using the HP-LEC method after P-injection direct synthesis polycrystalline. It is found that by carefully adjusting the thermal symmetry of the heating field and by further improving the quality of the polycrystalline, three inch and four inch twin-free Sn-doped InP crystals can be obtained even with a shoulder angle of up to 35/spl deg/-90/spl deg/, and defects caused by thermal decomposition appear on the surface of the crystals during pulling. For <111> LEC InP crystals, twin formation can be effectively suppressed by optimization of growth conditions, such as thermal field, doping concentration, etc. However, it is difficult to grow twin-free <100> LEC InP in a similar way. It is observed that the yield of single crystal <100> InP can be increased by controlling the ingot shape of a gradually increased diameter.

Indium phosphide crystal growth from phosphorus-rich melt

P-rich of InP crystals are rather difficult to achieve, due to the high phosphorus pressure at the melting point. By using the P-injection in-situ synthesis method, there is excessive phosphorus in the melt. In the conditions of M/sub In/ < M/sub In-s/, [P]/sub mol/>[In]/sub mol/, the melt might be P-rich. Since a high thermal stress exists in the LEC growth process with large temperature gradient, it is difficult to release stress, a large number of dislocations come into being around the pores. The pores are distributed in the ingots irregularly. The diameter of the pores is from <0.5 mm to 15 mm on the same wafer. The polished sample wafers with pores were characterized by PL mapping. Dislocations and pores in InP ingots are investigated by means of chemical etching, scanning electron microscopy (SEM). The experimental results show that the cell structures induced by movement and reaction of higher density dislocations exist at the edge of the pores. The EPD around the pores are higher than the other regions and the PL intensities are also inhomogeneous.

Study of semi-insulating LEC InP in China

Semi-Insulating InP is used in microelectronics devices and integrated opto-electronic circuits. The Chinese InP research team used a direct P-injection synthesis and LEC crystal growth method to prepare polycrystalline InP and to grow the undoped InP and Fe-doped SI-InP single crystal in the same puller. We can get very low concentration silicon in the ingots by using this method. And in the InP crystal the main impurity is silicon, which acts as a shallow donor in the crystal. The undoped InP has been found to be annealed into SI material around 900/spl deg/C. The Chinese InP research team present a model to explain the possible mechanisms of the Semi-Insulating behavior of bulk InP material. The physical properties of SI-InP have been studied. We have combined a variety of techniques such as FT-IR, PICTS, Hall, TDH, PL, PAS, and GDMS to investigate SI-InP. Most of the data can be explained by this model. Furthermore we compared the results of the MOCVD material, which grow on the annealed undoped SI-InP and on Fe-doped SI-InP.

Rapid P-injection in-situ synthesis and growth large diameter LEC InP single crystal

High purity InP is necessary for the preparation of high quality InP single crystal especially low Fe content semi-insulating and annealed undoped semi-insulating InP single crystal. In-situ phosphorus injection synthesis of InP has several advantages over the two-step process of compounding and growing in separate furnace. In 1982 it was reported by our group that around 500g InP was synthesized and semi-insulating InP single crystals grown in one step in 30-60 minutes. A large high pressure puller have been set up, which can be used to synthesize and grow large diameter InP single crystal in our laboratory. Now 3400g InP can be synthesized reproducible and single crystals can be grown in the puller. The red phosphorus used for synthesis is contained in two vessels, which can be manipulated separately during the synthesis process. The two phosphorus vessels are heated by the auxiliary heater and the phosphorus vapour is injected into the indium melt in the crucible. We have developed a process for the rapid synthesis of InP. The whole synthesis process only needs 60-70 minutes. The synthesized InP could be indium-rich, stoichiometric or phosphorus-rich which depend on the quantity of excess phosphorus and other conditions such as the temperature of indium melt in the crucible, the thermal field, phosphorus injection speed etc. After the synthesis, InP crystal can be pulled by the conventional LEC method. Twin-free 3-inch and 4-inch <100> InP single crystal can be obtained. The InP single crystal wafer is cut from the ingot for the measurement of electronic parameters. The carrier concentration of P-injection in-situ synthesis InP at T = 300 K is n = 2 /spl times/ 10/sup 15/ - 10/sup 16/ cm/sup -3/, the mobility is 3500 4900 cm/sup 2//Vs. These depend on the raw materials used. At T = 77 K the best result n = 2.36 /spl times/ 10/sup 15/ cm/sup -3/, the mobility is 4.8 /spl times/ 10/sup 4/ cm/sup 2//Vs. This kind of InP can be made semi-insulating with high temperature annealing or low iron doping levels.

Development of large diameter InP single crystal

A large quantity of high purity InP crystal material has been produced by the phosphorus in-situ injection synthesis and liquid encapsulated Czochralski (LEC) growth process. The in-situ process exhibits several advantages over the two-step process of compounding and growing in separate furnaces. About 2500-5000g stoichiometric poly InP is synthesized reproducibly by P-injection method in the high-pressure puller. Twin-f ree InP single crystals with diameter of 60-100 mm can be pulled after the synthesis.

Residual donors in undoped LEC InP

Undoped liquid encapsulated Czochralski (LEC) InP samples have been studied by Hall effect, glow discharge mass spectroscopy (GDMS) and infrared absorption spectroscopy. A systematic discrepancy has been found between the Hall electron concentration and net donor concentration measured by GDMS. The electron concentration is always higher than the net shallow donor concentration by about (3-6)/spl times/10/sup 15/ cm/sup -3/. A hydrogen indium vacancy complex donor defect V/sub In/H/sub 4/ was detected regularly by infrared absorption spectroscopy in all undoped LEC InP samples. The fact can be explained by taking into account the existence of the donor defect in as-grown undoped LEC-InP.